Color video camera for generating a Luminance signal with unattenuated harmonics

ABSTRACT

The outputs of N kinds of spectral response characteristics from an image sensor are passed through low-pass filters to obtain N kinds of outputs from the 1st through Nth, and the output signal of a pixel of interest having the Kth (1≦K≦N) spectral response characteristic is multiplied by the ratio of the low-pass filter output of the image sensor output at the coordinates of the pixel of interest to the Kth low-pass filter output at the coordinates of the pixel of interest, thereby the luminance signal with alleviated attenuation of the harmonics components is obtained.

This application is a divisional of allowed prior application Ser. No.08/485,908 filed on Jun. 7, 1995 and allowed Dec. 24, 1996 with U.S.Pat. No. 5,652,620, which is a divisional application of Ser. No.08/010,069 filed on Jan. 27, 1993 and issued on Sep. 12, 1995 with U.S.Pat. No. 5,450,124 the entire contents of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a color video camera, particularly tothe method of generating luminance signals thereof.

2. Description of Related Art

FIG. 1 shows an arrangement of color filters of an image sensordescribed, for example, on pages 76 through 82 of "National TechnicalReport", Vol. 31, No.1, February 1985, composed by Matsushita TechnoResearch Co., Ltd. and published by Ohmsha Publishing Co., Ltd. In FIG.1, Mg represents a pixel having a magenta color filter, G represents apixel having a green color filter, Cy represents a pixel having a cyancolor filter and Ye represents a pixel having a yellow color filter.FIG. 2 shows a part of a signal processing circuit of a color videocamera which employs an image sensor consisting of these color filtersarranged thereon. In FIG. 2, numeral 1 indicates a lens, numeral 2indicates an image sensor, numeral 3 indicates a band-pass filter (BPF),numeral 4 indicates a detector, numeral 5 indicates a one horizontalperiod delay circuit (1HDLY), numeral 6 indicates a switching circuitand numeral 45 indicates a low-pass filter (LPF).

The operation will now be described below. In FIG. 2, incident ray onthe lens 1 forms an image on the image sensor 2. In FIG. 1, an outputsignal from line n of the image sensor 2, consisting of a sequence of(Mg+Cy) and (G+Ye) being repeated, is denoted as Sn, and an outputsignal from line n+1 of the image sensor 2, consisting of a sequence of(Mg+Ye) and (G+Cy) being repeated, is denoted as S(n+1). Then Sn andS(n+1) are represented by the following equations.

    Sn=Yn+Cn·sin(ωt)+ . . .                     (1)

    S(n+1)=Y(n+1)+C(n+1)·sin(ωt)+ . . .         (2)

Where ω is the carrier frequency of the color signal which correspondsto double the horizontal pixel width. Yn and Y(n+1) in equations (1) and(2) represent the luminance signal components of line n and line n+1, Cnand C(n+1) represent the color difference signal components of line nand line n+1, respectively, and are given by the following equations.

    Yn=(Ye+G)+(Cy+Mg)=2R+3G+2B                                 (3)

    Y(n+1)=(Ye+Mg)+(Cy+G)=2R+3G+2B                             (4)

    Cn=(Cy+Mg)-(Ye+G)=2B-G                                     (5)

    C(n+1)=(Ye+Mg)-(Cy+G)=2R-G                                 (6)

The luminance signal components Yn, Yn+1 are obtained by passing theoutput of the image sensor 2 through the low-pass filter 45. The colordifference signal components Cn, C(n+1) are obtained by passing theoutput of the image sensor 2 through the band-pass filter 3 having acenter frequency ω and a detector 4. The output of the detector 4 gives2R-G and 2B-G appearing every two lines. These signals 2R-G, 2B-G whichappear on every other line are synchronized by the one horizontal perioddelay circuit 5 and the switching circuit 6.

In the conventional color video camera as described above, an outputsignal of the image sensor is passed through a low-pass filter to removethe modulated components of the color signal and obtain a luminancesignal, resulting in a problem of the harmonics of the luminance signalsbeing attenuated. Although aperture correction has been made byenhancing the rising edge and falling edge of the signal to improve theresolution, it causes an impression of unnatural enhancement.

FIG. 3 shows a block circuit diagram illustrating the circuit of a colorvideo camera employing a spatial offset of 3-chip CCD color camera whichis described, for example, on pages 1079 through 1085 of the "Journal ofTelevision Engineering Association", November 1986. In FIG. 3, numeral51 indicates a lens, numeral 52 indicates a refracting prism whichdecomposes incident ray into three colors of red, green and blue,numeral 53, 54, 55 indicate image sensors, numeral 56 indicates a redsignal amplifier, numeral 57 indicates a green signal amplifier, numeral58 indicates a blue signal amplifier, numeral 68 indicates a low-passfilter, numeral 71 indicates an adder and numeral 73 indicates ademultiplexer. FIG. 4 shows the constitution of output signals with theconventional method of spatial offset of 3-chip CCD color camera. InFIG. 4, G represents the signal of a green pixel, and RB represents thecomposite signal of red and blue pixels. Letter p indicates thehorizontal pixel width of the image sensor. Green image sensors and red,blue image sensors are arranged in the horizontal direction at intervalsof a half pixel width.

The operation will now be described below. In FIG. 3, incident ray onthe lens 51 is decomposed into red, green and blue by the refractingprism 52, with the light rays of respective colors forming images onimage sensors 53, 54, 55. Each of the image sensors 53, 54, 55 mixessignals of the upper and lower adjacent pixels to give one signaloutput. The output signals R, G, B of the image sensors 53, 54, 55 areamplified by the red signal amplifier 56, the green signal amplifier 57and the blue signal amplifier 58, respectively, so that the ratio of theoutput signals thereof becomes, in the case of NTSC system,R:G:B=0.30:0.59:0.11, to obtain R', G', B' signals. R' and B' are mixedin the adder 71 to obtain a signal RB which combines R' and B'. Thedemultiplexer 73 switches alternately between G' and RB to produce anoutput of luminance signal, which is passed through the low-pass filter68 to obtain a luminance signal Y. Consequently, the luminance signal Yis given by equation (7). ##EQU1##

In the conventional method of spatial offset of 3-chip CCD color camera,the purpose is set at improving the resolution. Although there arises noproblem in the case of such objects that have green signal and red-bluecombined signal in similar proportions, but vertical lines appear in thecase of objects which have significantly different proportions. Verticallines have been reduced by passing the green signal and red-bluecombined signal through a low-pass filter in the prior art, though ithas a problem of causing attenuation of harmonics in the luminancesignal. Thus resolution has been improved by enhancing the rising edgeand falling edge of a signal for aperture correction, resulting in aproblem of unnatural enhancement.

SUMMARY OF THE INVENTION

One object of the invention is to provide a color video camera which iscapable of alleviating the attenuation of the harmonics of luminancesignal.

Another object of the invention is to provide a color video camera madeof low cost circuits which is capable of producing high quality imagewith less attenuation of the harmonics of luminance signal.

Further another object of the invention is to provide a color videocamera which is capable of performing aperture correction withoutunnatural enhancement by means of simple circuits at a low cost.

In the color video camera of the invention, outputs from N kinds ofspectral-response characteristics from one image sensor are passedthrough a low-pass filter to obtain outputs of N kinds from 1st throughNth, and the output signal of a pixel of the Kth spectral-responsecharacteristic (1≦K≦N) is multiplied by the ratio of the low-pass filteroutput, produced from the output of the image sensor at the coordinateof the pixel, to the Kth low-pass filter output at the coordinate of thepixel, thereby to obtain the luminance signal with lessened attenuationof the harmonics.

In another color video camera of the invention, N kinds signals obtainedby adjusting the gain of the outputs from N kinds of image sensors arepassed through a low-pass filter to obtain outputs of N kinds from 1stthrough Nth, and the output signal of the Kth pixel (1≦K≦N) ismultiplied by the ratio of the low-pass filter output, produced from theoutput of the image sensor at the coordinate of the pixel, to the Kthlow-pass filter output at the coordinate of the pixel, thereby to obtainthe luminance signal with lessened attenuation of the harmonics.

In further another color video camera of the invention, outputs from Nkinds of spectral-response characteristics from one image sensor arepassed through the first low-pass filter to obtain outputs of N kindsfrom 1st through Nth, and the output signal of a pixel of the Kthspectral-response characteristic (1≦K≦N) is multiplied by the ratio ofthe first low-pass filter output, produced from the output of the imagesensor at the coordinate of the pixel, to the Kth output of the firstlow-pass filter at the coordinate of the pixel, thereby to calculate thefirst signal, which is fed to the band-pass filter to obtain a secondsignal for aperture correction, the image sensor output is fed to thesecond low-pass filter to obtain a third signal and the second signaland the third signal are combined to obtain a luminance signalcomponent, thereby performing aperture correction without unnaturalenhancement.

In further another color video camera of the invention, N kinds signalsobtained by adjusting the gain of the outputs from N kinds of imagesensors are passed through the first low-pass filter to obtain outputsof N kinds from 1st through Nth, and the output signal of the Kth pixel(1≦K≦N) is multiplied by the ratio of the first low-pass filter output,produced from the synthesized signals of the pixels of the respectivekinds at the coordinate of the pixel, to the Kth output of the firstlow-pass filter at the coordinate of the pixel, to calculate the firstsignal which is fed to the band-pass filter to obtain the second signalfor aperture correction, synthesized signal produced from N kinds ofsignals by adjusting the gain of the outputs of each image sensor is fedto the second low-pass filter to obtain the third signal, and the secondsignal and the third signal are synthesized to obtain the luminancesignal, thereby performing aperture correction without unnaturalenhancement.

The low-pass filter used in this invention may either be aone-dimensional low-pass filter consisting of a plurality of bit-shiftcircuits and an adder, or a two-dimensional low-pass filter consistingof a plurality of bit-shift circuits and a plurality of adders.

Use of a lookup table for division, a lookup table for logarithm, alookup table for power or the like simplifies the constitution of thesignal processing circuit.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of the arrangement of color filters of an imagesensor used in a color video camera.

FIG. 2 shows a part of signal processing circuit of the conventionalcolor video camera.

FIG. 3 shows a block circuit diagram illustrating a color video cameraof the conventional spatial offset of 3-chip CCD color camera system.

FIG. 4 shows the constitution of the output signals of the conventionalspatial offset of 3-chip CCD color camera system.

FIG. 5 shows a block circuit diagram illustrating the color video cameraof the present invention.

FIG. 6 shows the signals written in the field memory.

FIG. 7 shows the signals written in the two-dimensional memory.

FIG. 8 shows the signals written in the two-dimensional memory.

FIG. 9 shows the signals written in the two-dimensional memory.

FIG. 10 shows the signals written in the two-dimensional memory.

FIG. 11 shows the output signals of the two-dimensional low-pass filter.

FIG. 12 shows the output signals of the two-dimensional low-pass filter.

FIG. 13 shows the output signals of the two-dimensional low-pass filter.

FIG. 14 shows the output signals of the two-dimensional low-pass filter.

FIG. 15 shows a block circuit diagram illustrating another color videocamera of the present invention.

FIG. 16 shows a block diagram illustrating the constitution of thearithmetic logic unit.

FIG. 16A shows a block diagram illustrating another constitution of thearithmetic logic unit.

FIG. 17 shows the signals written in the one-dimensional memory.

FIG. 18 shows the signals written in the one-dimensional memory.

FIG. 19 shows the output signals of the one-dimensional low-pass filter.

FIG. 20 shows the output signals of the one-dimensional low-pass filter.

FIG. 21 shows the output signals of the one-dimensional low-pass filter.

FIG. 22 shows a block circuit diagram illustrating further another colorvideo camera of the present invention.

FIG. 23 shows a block circuit diagram illustrating further another colorvideo camera of the present invention.

FIG. 24 shows the constitution of the lookup table for division.

FIG. 25 shows the constitution of the lookup table for division.

FIG. 26 shows the constitution of the one-dimensional low-pass filter.

FIG. 27 shows a block circuit diagram illustrating further another colorvideo camera of the present invention.

FIG. 28 shows a block circuit diagram illustrating further another colorvideo camera of the present invention.

FIG. 29 shows a block circuit diagram illustrating the constitution ofthe arithmetic logic unit.

FIG. 30 shows the output signals of the two-dimensional low-pass filter.

FIG. 31 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 32 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 33 shows the constitution of the two-dimensional low-pass filter.

FIG. 34 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 35 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 36 shows a block circuit diagram illustrating the constitution ofthe arithmetic logic unit.

FIG. 37 shows the signals written in the one-dimensional memory.

FIG. 38 shows the signals written in the one-dimensional memory.

FIG. 39 shows the signals written in the one-dimensional memory.

FIG. 40 shows the output signals of the one-dimensional low-pass filter.

FIG. 41 shows the output signals of the one-dimensional low-pass filter.

FIG. 42 shows the output signals of the one-dimensional low-pass filter.

FIG. 43 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 44 shows a block circuit diagram illustrating the constitution ofthe arithmetic logic unit.

FIG. 45 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 46 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 47 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 48 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 49 shows the signals written in the two-dimensional memory.

FIG. 50 shows the signals written in the two-dimensional memory.

FIG. 51 shows the signals written in the two-dimensional memory.

FIG. 52 shows the output signals of the two-dimensional low-pass filter.

FIG. 53 shows the output signals of the two-dimensional low-pass filter.

FIG. 54 shows the output signals of the two-dimensional low-pass filter.

FIG. 55 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 56 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 57 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 58 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 59 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 60 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 61 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 62 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 63 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 64 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 65 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 66 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 67 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 68 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 69 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 70 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 71 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 72 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 73 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 74 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 75 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

FIG. 76 shows a block circuit diagram illustrating further another colorvideo camera of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described in detail below with reference to thedrawings which illustrate the preferred embodiments.

Embodiment 1

FIG. 5 shows the block circuit diagram illustrating the color videocamera in embodiment 1. In FIG. 5, numeral 1 indicates a lens, numeral 2indicates an image sensor, numeral 3 indicates a band-pass filter (BPF),numeral 4 indicates a detector, numeral 5 indicates a one horizontalperiod delay circuit (1HDLY), numeral 6 indicates a switching circuit,numeral 7 indicates an A/D converter, numeral 8 indicates a fieldmemory, numeral 9 indicates a multiplexer, numerals 10, 11, 12, 13indicate two-dimensional memories, numerals 14, 15, 16, 17 indicatetwo-dimensional low-pass filters (two-dimensional LPF), numeral 42indicates an arithmetic logic unit and numeral 43 indicates a matrixcircuit.

The operation will now be described below. Incident ray on the lens 1forms an image on the image sensor 2 having photoelectric transducerswhich have different spectral-response characteristics and are arrangedon a two-dimensional plane. The output of the image sensor 2 isconverted from analog to digital signal by the A/D converter 7 and issupplied to the field memory 8. The image sensor 2 shown in FIG. 5 mixesthe signals of two upper and lower adjacent pixels to give an output.Mixed signals are written in the field memory 8 as one signal. FIG. 6partially illustrates the configuration of writing the signals from theimage sensor 2 in the field memory 8. In FIG. 6, MC represents a signalwhich combines the magenta pixel signal and cyan pixel signal, GYrepresents a signal which combines the green pixel signal and yellowpixel signal, MY represents a signal which combines the magenta pixelsignal and yellow pixel signal and GC represents a signal which combinesthe green pixel signal and cyan pixel signal. The multiplexer 9 suppliesthe MC, GY, MY, GC signals separately to the two-dimensional memories10, 11, 12, 13, respectively. FIG. 7, FIG. 8, FIG. 9, FIG. 10 show theconfiguration of signals written in the two-dimensional memories 10, 11,12, 13. The signals shown in these drawings are smoothed by thetwo-dimensional low-pass filters 14, 15, 16, 17. FIG. 11, FIG. 12, FIG.13, FIG. 14 show the outputs of the two-dimensional low-pass filters 14,15, 16, 17. LPF in the drawing represents a low-pass filter output.

Arithmetic logical operation in the arithmetic logic unit 42 will bedescribed below. In FIG. 6, the value of an output signal, when colorfilter of MC, GY, MY are assumed to be located at the position of GC ofrow s and column t for example, is calculated by equations (8) through(10).

    MC(s,t)=GC(s,t)×(MCLPF(s,t)/GCLPF(s,t))              (8)

    GY(s,t)=GC(s,t)×(GYLPF(s,t)/GCLPF(s,t))              (9)

    MY(s,t)=GC(s,t)×(MYLPF(s,t)/GCLPF(s,t))              (10)

It is not necessary to calculate the value of GC(s,t) because equation(11) holds.

    GC(s,t)=GC(s,t)                                            (11)

When it is assumed that a color filter of kind K (K is either MC, GY, MYor GC) is located at the position (s, t) of a color filter of kind J (Jis either MC, GY, MY or GC), color signal K (s,t) is calculated byequation (12). (s,t) in the case of this embodiment indicates thecoordinates of the field memory 8 shown in FIG. 6.

    K(s,t)=J(s,t)×(KLPF(s,t)/JLPF(s,t))                  (12)

Matrix computation in the matrix circuit 43 is described below.Luminance signal component Y at the position of GC at row s, column t inFIG. 6 is calculated by equation (13).

    Y=(MC(s,t)+GY(s,t)+MY(s,t)+GC(s,t))/4                      (13)

The principle of calculating Y signal in this embodiment will bedescribed below. If modulation component of a color signal is removed bypassing the output signal of the image sensor through the low-passfilter as in the prior art, harmonics of the luminance signal will beattenuated. The method of this embodiment assumes that color change isnot significant in a localized region. This implies that ratios betweensignals of different colors (MC, GY, MY, GC) are approximately equal toeach other in the localized region. Ratios between signals of differentcolors MC, GY, MY and GC in a localized region are given by the ratiosbetween two-dimensional low-pass filter outputs of MC, GY, MY and GC.When a color filter of MC is located at the position GC of row s, columnt as shown by equation (8), for example, the ratio is obtained bymultiplying GC(s,t) by the ratio of MC to GC at the localized region(ratio of two-dimensional low-pass filter output of MC signal totwo-dimensional low-pass filter output of GC signal). Equations (9),(10), (11) are also obtained similarly. By calculating Y signal byequation (13) using MC, GY, MY, GC obtained from equations (8), (9),(10), (11), modulation component of the color signal can be removedwithout using the low-pass filters. Because modulation component of thecolor signal is removed without using the low-pass filters, it is madepossible to alleviate the attenuation of the harmonics of the luminancesignal.

Embodiment 2

FIG. 15 shows embodiment 2 of the invention where portions denoted withthe same numerals as those in FIG. 5 represent the same or correspondingportions. In FIG. 15, numerals 18, 19 represent one-dimensionalmemories, numerals 20, 21, 22 represent one-dimensional low-pass filters(LPF) and numeral 23 represents an arithmetic logic unit. FIG. 16 showsthe internal constitution of the arithmetic logic unit 23, which has ademultiplexer 24, a divider 25 and a multiplier 26.

The operation will now be described below. Similarly to the case ofembodiment 1 as shown in FIG. 6, signal from the image sensor 2 iswritten in the field memory 8. The multiplexer 9 supplies MC, GY signalsand MY, GC signals alternately to the memories 18, 19 via line n andline n+1. FIG. 17 and FIG. 18 show the configuration of signals writtenin the memories 18, 19. The signals shown in these drawings are smoothedby the low-pass filters 20, 21. FIG. 19, FIG. 20 show the outputs of thelow-pass filters 20, 21. Output of the image sensor 2 is converted fromanalog to digital signal which is passed through the low-pass filter 22,to obtain low-pass filter output of Y signal. FIG. 21 shows the outputof the low-pass filter 22, where LPF in the drawing is a symbolrepresenting a low-pass filter output.

Arithmetic logical operation of the arithmetic logic unit 23 will bedescribed below. The low-pass filter output of Y signal is fed to thedivider 25 as the dividend. The demultiplexer 24 switches, in the caseof line n, to the low-pass filter output of MC if the pixel is MC pixelor to the low-pass filter output of GY if the pixel is GY pixel and, inthe case of line n+l, switches to the low-pass filter output of MY ifthe pixel is MY pixel or to the low-pass filter output of GC if thepixel is GC pixel, with the output thereof being fed to the divider 25as the divisor. The output of the divider 25 is supplied to themultiplier 26 as the input. The output signal of the pixel is suppliedto the multiplier 26. As a result, the output of the multiplier 26 isobtained as Y signal at the pixel of interest.

In FIG. 17, luminance signal component Y (t) at the position of colorfilter GC of column t, for example, is calculated by equation (14)below.

    Y(t)=GC(t)×(YLPF(t)/GCLPF(t))                        (14)

Luminance signal component Y (t) at the position t of color filter ofkind K (K is either MC, GY, MY or GC) is calculated by equation (15)below. In this embodiment, letter t represents the coordinate of memory18 shown in FIG. 17 in case the pixel is color filter of GC, GY, orrepresents the coordinate of memory 19 shown in FIG. 18 in case thepixel is MY, MC.

    Y(t)=K(t)×(YLPF(t)/KLPF(t))                          (15)

Principle of calculating Y signal in embodiment 2 will be describedbelow. This method assumes that color change in the localized region isnot significant. This implies that the ratios of signals of respectivecolors (MC, GY, MY, GC) to Y signal are approximately equal in alocalized region. Ratios of signals of different colors MC, GY, MY andGC to Y signal in a localized region are given by the ratios of low-passfilter outputs of MC, GY, MY and GC to the low-pass filter output of Ysignal.

For example, luminance signal component Y(t) at the position of GC ofcolumn t as shown by equation (14) is obtained by multiplying GC(t) bythe ratio of Y to GC (ratio of the low-pass filter output of Y signal tothe low-pass filter output of GC signal) in the localized region.

While harmonics of luminance signal is attenuated in the conventionalmethod as described for embodiment 1, modulated components of colorsignal can be removed without attenuating the harmonics of the luminancesignal in embodiment 2 as in embodiment 1.

Embodiment 3

Although constitution of the color video camera in embodiment 3 is thesame as that of embodiment 2 (FIG. 15), method of calculating Y signalin the arithmetic logic unit 23 is different.

Arithmetic operation in the arithmetic logic unit 23 will be describedbelow. In FIG. 17, if each signal is made up of eight bits to representthe hue in 256 steps, for example, and value 1 of LSB (Least SignificantBit) is employed as a constant, luminance signal component Y(t) at theposition of color filter GC of column t is calculated by equation (16)as shown below.

    Y(t)=(GC(t)+1)×((YLPF(t)+1)/(GCLPF(t)+1))-1          (16)

Luminance signal component Y (t) at the position t of color filter ofkind K (K is either MC, GY, MY or GC) is given by equation (17) below.

    Y(t)=(K(t)+1)×((YLPF(t)+1)/(KLPF(t)+1))-1            (17)

There may arise such a case as calculation of division becomesimpossible due to the divisor being zero, or a great calculation erroris caused by the divisor being not equal to but near zero if calculatingwith a small number of bits. In such a case, calculation error can bedecreased by employing value 1 of LSB as in embodiment 3.

Embodiment 4

FIG. 22 shows a block circuit diagram illustrating a color video cameraof embodiment 4. In FIG. 22, portions denoted with the same numerals asthose in FIG. 15 represent the same portions. Numeral 27 represents acomparator.

The operation will now be described below. An output signal of anappropriate pixel in the vicinity of the pixel of interest is read fromthe field memory 8 and is fed to the comparator 27. If the differencebetween the output signals of pixels of the same kind is beyond aparticular threshold, it is determined that the spatial frequency of theimage is high and, if the difference is within the threshold, it isdetermined that the spatial frequency of the image is low. In a portionwhere the spatial frequency of the image is high, the luminance signalis calculated similarly to embodiment 2 and, in a portion where thespatial frequency of the image is low, the luminance signal iscalculated from the weighted averaging value of the pixels of N kindsaround the pixel of interest.

The arithmetic logic unit 23 operates as in embodiment 2 in the portionof high spatial frequency and, in the portion of low spatial frequency,luminance signal component Y(t) is calculated by equation (18) at theposition of GC color filter in column t in FIG. 17 and at the positionwhere there is no output signal of column t by equation (18).

    Y(t)=MY(t-1)/4+GC(t)/2+MY(t+1)/4                           (18)

Assuming the position of the pixel being t, the kind of color filter ofthe pixel of interest being J (J is either MC, GY, MY or GC), and thekind of color filter of the right and left adjacent pixels of the pixelof interest being K (K is either MC, GY, MY or GC), the luminance signalcomponent Y(t) is calculated by equation (19).

    Y(t)=K(t-1)/4+J(t)/2+K(t+1)/4                              (19)

As described above, the edge-like effects due to the image contrastbecoming exaggerated producing emphasized patches of light and dark, inthe low frequency components arising when the number of bits ofcalculated data is reduced, can be suppressed by employing differentmethods in calculating the luminance signals between portions of highspatial frequency and low spatial frequency.

Embodiment 5

Although the constitution of the color video camera in embodiment 5 isthe same as that of embodiment 4 (FIG. 22), signal processing proceduresin the arithmetic logic unit 23 and in the comparator 27 are different.

In embodiment 5, difference in the output signals between right and leftadjacent pixels of the pixel of interest and the particular thresholdare compared. If the difference between the output signals is greaterthan the threshold, it is determined that the portion has a high spatialfrequency and the operation of aforementioned embodiment 2 is carriedout, and, if the difference between the output signals is less than thethreshold, it is determined that the portion has a low spatialfrequency, and the operation of aforementioned embodiment 4 is carriedout.

Arithmetic operation of the comparator 27 will be described below.Assuming that, for example, the color filter located at row s, column tis GC and the color filters located at right and left adjacent pixels ofthe pixel of interest are MY, the result of the calculation by equation(20) below and the threshold are compared to select one of the twoequations to generate the luminance signals.

    |MY(t-1)-MY(t+1)|                        (20)

Assuming that the position of the pixel of interest is t and the kind ofcolor filters of the right and left adjacent pixels of the pixel ofinterest being K (K is either MC, GY, MY or GC), result of thecalculation by equation (21) below and the threshold are compared toselect one of two equations to generate the luminance signals.

    |K(t-1)-K(t+1)|                          (21)

Embodiment 6

FIG. 23 shows a block circuit diagram of the color video camera inembodiment 6. In FIG. 23, numerals which are the same as those in FIG.15 indicate the identical portions. Numeral 28 represents a lookup tablefor division.

Since the equation of calculation described in embodiment 2 includes adividing operation, the lookup table for division 28 is used inembodiment 6. When 55/13 is to be calculated with 5-bit input to thelookup table for division 28 assuming that 8-bit inputs of 55 (00110111)and 13 (00001101) are given as shown in FIG. 24, for instance, upperfive bits of each input are checked successively starting with the mostsignificant bit to search for a bit of a value 1 and, if found, it ismade the new most significant bit with the five bits including this andthose that follow handled as the input. Namely, inputs are bit-shiftedto obtain the most effective five bits such as 27 (11011) and 13(01101). Then output 2 (00010) which corresponds to the result ofdivision of the two inputs is obtained from the lookup table fordivision 28, and the number of digits thereof is raised by the number ofdigits which were cut off from the dividend, thereby to obtain 4 as theresult of the arithmetic operation.

Assume m-bit inputs x and y and n-bit input to the lookup table fordivision 28 (m>n), and the most significant bit of the input is checkedto see if it is 1. If it is 0, lower bits are checked successivelystopping at the nth bit. If x has 1 in the ath bit (m≧a≧n) and y has 1in the bth bit (m≧b≧n), these bits are regarded as the most significantbits thereby to obtain the upper n bits x' and y'. Namely, x' and y' arethe most effective n bits with the less significant bits thereof beingdiscarded as shown by equations (22) and (23).

    x'=x>>(a-n)                                                (22)

    y'=y>>(b-n)                                                (23)

    z'=x'/y'                                                   (24)

Where >> represents a bit shift operation, with the digits of x beingreduced by a-n bits and the digits of y being reduced by b-n bits. Withthe resultant x' and y' being fed as the inputs, an output z' isobtained from the lookup table for division 28, and bit shift operationcorresponding to the number of bits which were cut off from the dividendand divisor is applied to z'. Namely, operation of equation (25) iscarried out to obtain the result z.

    z=z'>>(b-a)                                                (25)

Let the output of the lookup table for division 28 be a number of eightbits, for instance, then dividing operation of the upper seven bits ofthe two inputs require the lookup table for division 28 to have acapacity of 131072 bits, while similar result can be obtained with thelookup table for division 28 having a capacity of 8192 bits when mosteffective five bits of inputs are used in the dividing operation. As aresult, circuit composition of embodiment 6 is made simpler.

Embodiment 7

Although the composition of the color video camera in embodiment 7 isthe same as that of embodiment 6 (FIG. 23), signal processing operationsin the arithmetic logic unit 23 and the lookup table for division 28 aredifferent.

The operation will now be described below. Lookup table for division 28in embodiment 7 has five bits above decimal point and five bits belowdecimal point. In calculating the division of 55/13 with 5-bit inputs tothe lookup table for division 28 when 8-bit inputs of 55 (00110111) and13 (00001101) are given as shown in FIG. 25, for instance, inputs arebit-shifted to the most effective five bits such as 27 (11011) and 13(01101). Then output 66 (0001000010) which corresponds to the result ofthe division of the two inputs is obtained from the lookup table fordivision 28, and its number of digits is raised by the number of digitswhich were cut off from the dividend. Thus 132 is obtained as the resultof the arithmetic operation. Then this result of the division is used inthe multiplication by the equation described in embodiment 2, with thelower five bits being cut off to discard the fractional part of thelookup table for division 28. Assuming the value of the multiplier to be11, 45 is obtained from the above calculation.

Assume that m-bit inputs x and y are given, an n-bit input is fed to thelookup table for division 28 (m>n) to obtain a 2n-bit output comprisingan integral part of n bits and a fractional part of n bits (m>n), xincludes the first 1 in the ath bit from the MSB (m≧a≧n), y includes thefirst 1 in the bth bit from the MSB (m≧b≧n), most effective n-bit partsof x and y are x' and y', respectively, which are fed to the lookuptable for division 28 as inputs to obtain an output z', and bit shift isapplied corresponding to the number of bits which were cut off thedividend and divisor, to obtain z as the result of calculation. Then thevalue of z is used in the multiplication described in embodiment 2 withthe result being shifted down by n bits to discard the fractional partof the lookup table for division 28. Assuming the value of multiplierbeing p, the result of calculation q is given by equation (26) as shownbelow.

    q=(p×z)>>n                                           (26)

As described above, precision of calculation can be increased byobtaining an output with the number of bits twice that of the input fromthe lookup table for division 28 to obtain the fractional part as theoutput, then multiplying with this output.

Embodiment 8

The composition of the color video camera in embodiment 8 is the same asthat of embodiment 2 (FIG. 15). In embodiment 8, low-pass filter is usedas a digital filter. The low-pass filter is made up of only bit shiftcircuits such as, for example, the number of horizontal taps being setto 5 with weightings 1/8, 1/4, 1/4, 1/4 and 1/8. FIG. 26 shows thecomposition of the one-dimensional low-pass filter. In FIG. 26, 101through 104 are one clock delay circuits (1CLKDLY), 105 and 109 are3-bit shift circuits, 106 through 108 are 2-bit shift circuits, and 110is an adder.

Assume that an image sensor output S(t+2) is fed to the one-dimensionallow-pass filter of such a composition. The 3-bit shift circuit 105 feedsS(t+2)/8 to the adder 110. Output S(t+1) of the image sensor deliveredat the time one clock earlier is fed via the one clock delay circuit 101to the 2-bit shift circuit 106 to obtain an output S(t+1)/4. Similarly,outputs S(t)/4, S(t-1)/4 and S(t-2)/8 are obtained from the 2-bit shiftcircuits 107, 108 and the 3-bit shift circuit 109. Accordingly, theoutput of the adder 110 becomes such an output as represented byequation (27), and low-pass filter output YLPF(t) for the image sensoroutput at position t of the pixel of interest can be obtained.

    YLPF(t)=S(t+2)/8+S(t+1)/4+S(t)/4+S(t-1)/4+S(t-2)/8         (27)

While the process described above is applied to the low-pass filteroutput for the image sensor output, the low-pass filter output of thepixel of the Jth color filter at position t of the pixel of interest canbe obtained by using a two clock delay circuit instead of one clockdelay circuit, because the Jth color filters are arranged at every otherpixel.

Embodiment 9

Although the composition of the color video camera in embodiment 9 isthe same as that of embodiment 2 (FIG. 15), method of calculating theluminance signal in the arithmetic logic unit 23 is different.

In embodiment 3, luminance signal is obtained by adding 1 to each of themultiplier, divisor and dividend and subtracting 1 from the result ofcalculation to minimize the calculation error, as expressed by theequations (16) and (17). However, as the number 1 is LSB which has nosignificant effect on the result of calculation, subtraction of 1 at theend may be omitted for the simplification of the circuit. Embodiment 9is an example of such simplification. Luminance signal component Y(t) atthe position of GC color filter of column t is calculated by theequation (28) below.

    Y(t)=(GC(t)+1)×((YLPF(t)+1)/(GCLPF(t)+1))            (28)

Luminance signal component Y(t) at position t of color filter of kind K(K is either MC, GY, MY or GC) is expressed by the equation (29) below.

    Y(t)=(K(t)+1)×((YLPF(t)+1)/(KLPF(t)+1))              (29)

Embodiment 9 is also capable of reducing the calculation error similarlyto embodiment 3.

Embodiment 10

FIG. 27 shows a block circuit diagram of the color video camera inembodiment 10. In FIG. 27, numerals which are the same as those in FIG.15 indicate the identical portions. Numeral 29 represents a lookup tablefor logarithm and numeral 30 represents a lookup table for power.

The operation will now be described below. Luminance signal componentY(t) in case the kind of color filter of the pixel at position t is K (Kis either MC, GY, MY or GC) is given by the equation (29) below asdescribed in embodiment 9. Now apply logarithmic conversion with base xin equation (29) as shown in equation (30), where represents power.##EQU2##

If all coefficients used in equation (30) are given in 8-bit numbers andthe output of the lookup table for logarithm 29 is given with 10 bits,the capacity requirement is 2560 bits. After calculating the logarithmicpart by means of the lookup table for logarithm 29, addition andsubtraction are carried out to calculate the power. Because the powercan be represented sufficiently with 11 bits, 8-bit output from thelookup table for power 30 requires a capacity of 16384 bits.Consequently, calculation of the equation (29) can be done with a lookuptable which has a capacity of 18944 bits in total, making it possible tofurther simplify the circuit composition.

Although embodiment 10 is described in a case where luminance signal iscalculated from the equation of embodiment 9, it is a matter of coursethat the method of calculation which employs the lookup table forlogarithm and the lookup table for power may be applied to embodiment 2.

Embodiment 11

FIG. 28 shows a block circuit diagram of the color video camera inembodiment 11. In FIG. 28, numerals which are the same as those in FIG.5 indicate the identical portions and will not be explained here. InFIG. 28, numeral 31 represents a two-dimensional low-pass filter (LPF)for luminance signal Y and numeral 32 represents an arithmetic logicunit. FIG. 29 shows the internal construction of the arithmetic logicunit 32 which has a demultiplexer 33, a divider 34 and a multiplier 35.

The operation will now be described below. Basic operation is the sameas that of embodiment 1. The output of the image sensor is fed from thefield memory 8 to the two-dimensional low-pass filter 31, and outputYLPF of the two-dimensional low-pass filter as shown in FIG. 30 isobtained.

The arithmetic operation in the arithmetic logic unit 32 will bedescribed below. Two-dimensional low-pass filter output of Y signal isfed to the divider 34 as the dividend. The demultiplexer 33 switches tothe two-dimensional low-pass filter output of MC if the pixel ofinterest is MC pixel, to the two-dimensional low-pass filter output ofGY if the pixel of interest is GY pixel, to the two-dimensional low-passfilter output of MY if the pixel of interest is MY pixel, or to thetwo-dimensional low-pass filter output of GC if the pixel of interest isGC pixel, with the output being fed to the divider 34 as the divisor.The output of this divider 34 is fed to the multiplier 35 as the input.The output signal of the pixel of interest is also fed to the multiplier35 as the input. Thus the output of the multiplier 35 is obtained as theluminance signal Y of the pixel of interest.

Embodiment 11 is an example of using two-dimensional low-pass filtersinstead of one-dimensional low-pass filters in embodiment 2. In FIG. 6,luminance signal component Y(s,t) at the position of color filter GC ofrow s, column t is calculated by equation (31).

    Y(s,t)=GC(s,t)×(YLPF(s,t)/GCLPF(s,t))                (31)

Luminance signal component Y(s,t) at the position (s,t) of color filterof kind K (K is either MC, GY, MY or GC) is given by the equation (32)below, where (s,t) represents the coordinates of the field memory 8.

    Y(s,t)=K(s,t)×(YLPF(s,t)/KLPF(s,t))                  (32)

Calculation of Y signal in this embodiment is basically the same as thatof embodiment 2, and is capable of eliminating the modulated componentof the color signal without reducing the harmonics of the luminancesignal.

Embodiment 12

Although the composition of the color video camera in embodiment 12 isthe same as that of embodiment 11 (FIG. 28), method of calculating Ysignal in the arithmetic logic unit 32 is different.

The arithmetic operation in the arithmetic logic unit 32 will bedescribed below. In FIG. 6, if each signal is made up of eight bits torepresent the hue in 256 steps, for example, and value 1 of LSB isemployed as a constant, luminance signal component Y(s,t) at theposition of color filter GC of row s, column t is calculated by equation(33) as shown below.

    Y(s,t)=(GC(s,t)+1)×((YLPF(s,t)+1)/GCLPF(s,t)+1))-1   (33)

Luminance signal component Y(s,t) at position (s,t) of color filter ofkind K (K is either MC, GY, MY or GC) is given by the equation (34)below.

    Y(s,t)=(K(s,t)+1)×((YLPF(s,t)+1)/(KLPF(s,t)+1))-1    (34)

Embodiment 13

FIG. 31 shows a block circuit diagram of the color video camera inembodiment 13. In FIG. 31, symbols which are the same as those in FIG.28 indicate the identical portions and numeral 27 represents acomparator which resembles that of FIG. 22 (embodiment 4).

The operation will now be described below. As in the case of embodiment4, the difference between output signals of pixels of the same kindwhich are fed to the comparator 27 from the field memory 8 is comparedto a particular threshold to determine whether the spatial frequency ofthe image is high or low. In a portion of high spatial frequency,luminance signal is calculated similarly to embodiment 11 and, in aportion of low spatial frequency, luminance signal is calculated fromthe weighted averaging value of the outputs of the pixels of N kinds inthe vicinity of the pixel of interest.

The arithmetic logic unit 32 operates similarly to that in embodiment 11in the portion of high spatial frequency. In a portion of low spatialfrequency, for example, luminance signal component Y(s,t) at theposition of color filter GC of row s, column t in FIG. 6 is calculatedby equation (35). ##EQU3##

Assuming the position of the pixel of interest as (s,t), kind of colorfilter of the pixel of interest as J (J is either MC, GY, MY or GC),kind of the color filter of the right and left adjacent pixels of thepixel of interest as K (K is either MC, GY, MY or GC), kind of the colorfilter of the upper and lower adjacent pixels of the pixel of interestas L (L is either MC, GY, MY or GC), and the kind of the color filter ofthe diagonally adjacent pixels of the pixel of interest as M (M iseither MC, GY, MY or GC), then luminance signal component Y(s,t) iscalculated by the equation (36) below. ##EQU4##

Embodiment 14

Although the composition of the color video camera in embodiment 14 isthe same as that of embodiment 13 (FIG. 31), signal processingoperations in the arithmetic logic unit 32 and in the comparator 27 aredifferent.

In embodiment 14, difference between the output signals of right andleft pixels or between the output signals of the upper and lower pixelsof the pixel of interest is compared to a particular threshold. And itis determined that the portion has high spatial frequency if thedifference between the output signals is greater than the threshold, andaccordingly the operation in embodiment 11 is carried out, and, it isdetermined that the portion has low spatial frequency if the differencebetween the output signals is less than the threshold, and accordinglythe operation in embodiment 13 is carried out.

For example, the results of the calculations described below arecompared to the threshold at the position of the color filter of GC atrow s, column t in FIG. 6, to select one of the methods of generatingluminance signal.

    |MY(s,t-1)-MY(s,t+1)|                    (37)

    |GY(s-1,t)-GY(s+1,t)|                    (38)

Assuming the position of the pixel of interest as (s,t), the kind of thecolor filter of right and left adjacent pixels of the pixel of interestas J (J is either MC, GY, MY or GC), and the kind of the upper and loweradjacent pixels of the color pixel of interest as K (K is either MC, GY,MY or GC), the results of the calculations below are compared to thethreshold to select one of the methods of generating luminance signal.

    |J(s,t-1)-J(s,t+1)|                      (39)

    |K(s-1,t)-K(s+1,t)|                      (40)

Embodiment 15

Although the composition of the color video camera in embodiment 15 isthe same as that of embodiment 13 (FIG. 31), signal processingoperations in the arithmetic logic unit 32 and in the comparator 27 aredifferent.

In embodiment 15, difference between the output signals of the pixels ofthe same kind of spectral response characteristic in the vicinity of thepixel of interest is compared to a particular threshold. And it isdetermined that the portion has high spatial frequency if the differencebetween the output signals is greater than the threshold, and theoperation of embodiment 11 is carried out, and, it is determined thatthe portion has low spatial frequency if the difference between theoutput signals is less than the threshold, and the operation ofembodiment 13 is carried out.

For example, assuming that the color filter at the position ofcoordinate (s,t) of the pixel of interest is GC, the color filter at thepositions of the right and left adjacent pixels of the pixel of interestis MY, the color filter at the positions of the upper and lower adjacentpixels of the pixel of interest is GY, and the color filter at thepositions of the diagonally adjacent pixels of the pixel of interest isMC as shown in FIG. 6, then the results of the calculations below arecompared to the threshold to select one of the methods of generatingluminance signal.

    |MY(s,t-1)-MY(s,t+1)|                    (41)

    |GY(s-1,t)-GY(s+1,t)|                    (42)

    MC(s-1,t-1)-MC(s+1,t+1)|                          (43)

    MC(s-1,t+1)-MC(s+1,t-1)|                          (44)

Assuming the position of the pixel of interest as (s,t), the kind of thecolor filter of the right and left adjacent pixels of the pixel ofinterest as J (J is either MC, GY, MY or GC), the kind of the colorfilter of the upper and lower adjacent pixels of the color pixel ofinterest as K (K is either MC, GY, MY or GC), and the kind of the colorfilter of the diagonally adjacent pixels of the pixel of interest as L(L is either MC, GY, MY or GC), then the results of the calculationsbelow are compared to the threshold to select one of the methods ofgenerating luminance signal.

    |J(s,t-1)-J(s,t+1)|                      (45)

    |K(s-1,t)-K(s+1,t)|                      (46)

    |L(s-1,t-1)-L(s+1,t+1)|                  (47)

    |L(s-1,t+1)-L(s+1,t-1)|                  (48)

Embodiment 16

Although the composition of the color video camera in embodiment 16 isthe same as that of embodiment 13 (FIG. 31), signal processingoperations in the arithmetic logic unit 32 and in the comparator 27 aredifferent.

In embodiment 16, difference between the output signals of thediagonally adjacent pixels interposing the pixel of interest is comparedto a particular threshold. And it is determined that the portion hashigh spatial frequency if the difference between the output signals isgreater than the threshold, and the operation in embodiment 11 iscarried out, and, it is determined that the portion has low spatialfrequency if the difference between the output signals is less than thethreshold, and the operation in embodiment 13 is carried out.

For example, the results of the calculations shown below are compared tothe threshold at the position of the color filter of GC at row s, columnt in FIG. 6, to select one of the methods of generating luminancesignal.

    |MC(s-1,t-1)-MC(s+1,t+1)|                (49)

    |MC(s+1,t-1)-MC(s-1,t+1)|                (50)

Assuming the position of the pixel of interest as (s,t), the kind of thediagonally adjacent pixels of the color filter of the pixel of interestas J (J is either MC, GY, MY or GC), the results of the calculationsshown below are compared to the threshold to select one of the methodsof generating luminance signal.

    |J(s-1,t-1)-J(s+1,t+1)|                  (51)

    |J(s+1,t-1)-J(s-1,t+1)|                  (52)

Embodiment 17

FIG. 32 shows a block circuit diagram of the color video camera inembodiment 17. Symbols which are the same as those of FIG. 28 indicatethe identical portions and numeral 28 represents a lookup table fordivision which is similar to that of FIG. 23 (embodiment 6).

The operation in the lookup table for division 28 is the same as that ofembodiment 6, and will not be described here.

Embodiment 18

Application of the calculation method of embodiment 7 with respect toembodiment 6 to the above embodiment 17 is the embodiment 18. Theoperation in embodiment 18 is the same as that of embodiment 7, and willbe omitted.

Embodiment 19

The composition of the color video camera in embodiment 19 is the sameas that of embodiment 11 (FIG. 28). In embodiment 19, a two-dimensionallow-pass filter is used as a digital filter. The filter is made up ofonly bit shift circuits such as, for example, the number of horizontaltaps is set to 5, number of vertical taps being 3, the weightings are1/8, 1/4, 1/4, 1/4, 1/8 for the horizontal direction and 1/4, 1/2, 1/4,for the vertical direction. FIG. 33 shows the composition of thetwo-dimensional low-pass filter. In FIG. 33, 201 and 202 are onehorizontal period delay circuits (1HDLY), 204 is a 1-bit shift circuit(1B SHIFT), 203, 205, 219 through 221, 224 through 226 and 229 through231 are 2-bit shift circuits (2B SHIFT), 218, 222, 223, 227, 228, 232are 3-bit shift circuits (3B SHIFT), 206 through 217 are one clock delaycircuits (DLY) and 233 through 236 are adders.

Assume that an image sensor output S(s+1,t+2) is fed to thetwo-dimensional low-pass filter of such a composition. The output of the2-bit shift circuit 203 is S(s+1,t+2)/4 and the output of the 3-bitshift circuit 218 is S(s+1,t+2)/32. Output S(s+1,t+1)/4 of the imagesensor delivered at the time one clock earlier is fed via the one clockdelay circuit 206 to the 2-bit shift circuit 219 to obtain an outputS(s+1,t+1)/16. Similarly, outputs S(s+1,t)/16, S(s+1,t-1)/16 andS(s+1,t-2)/32 are obtained from the 2-bit shift circuits 220, 221 andthe 3-bit shift circuit 222. Accordingly, the output of the adder 233 isgiven as Y'LPF(s+1,t) expressed by equation (53).

    Y'LPF(s+1,t)=S(s+1,t+2)/32+S(s+1,t+1)/16+S(s+1,t)/16+S(s+1,t-1)/16+S(s+1,t-2)/32                                                      (53)

Similarly, the output of the adder 234 is given as Y'LPF(s,t) expressedby equation (54).

    Y'LPF(s,t)=S(s,t+2)/16+S(s,t+1)/8+S(s,t)/8+S(s,t-1)/8+S(s,t-2)/16(54)

Similarly, the output of the adder 235 is given as Y'LPF(s-1,t)expressed by equation (55).

    Y'LPF(s-1,t)=S(s-1,t+2)/32+S(s-1,t+1)/16+S(s-1,t)/16+S(s-1,t-1)/16+S(s-1,t-2)/32                                                      (55)

Accordingly, two-dimensional low-pass filter output YLPF(s,t) of theimage sensor output at the position (s,t) of the pixel of interest canbe obtained in the adder 236 as shown by equation (56).

    YLPF(s,t)=Y'LPF(s+1,t)+Y'LPF(s,t)+Y'LPF(s-1,t)             (56)

Although the described above are two-dimensional low-pass filter outputsof image sensor outputs, the two-dimensional low-pass filters of the Jthcolor filters at the position (s,t) of the pixel of interest are made ofthe Jth color filters which are arranged alternately at every otherpixel in both horizontal and vertical directions. Therefore use of a twoclock delay circuit instead of a one clock delay circuit, and a twohorizontal period delay circuit instead of a one horizontal period delaycircuit will serve the purpose.

Embodiment 20

Although the composition of the color video camera in embodiment 20 isthe same as that of embodiment 11 (FIG. 28), method of calculating theluminance signal in the arithmetic logic unit 32 is different.

In embodiment 12, a luminance signal is obtained by adding 1 to each ofthe multiplier, divisor and dividend and subtracting 1 from the resultof calculation at the end to minimize the calculation error, as shown inequations (33) and (34). However, as the number 1 is LSB which has nosignificant effect on the result of calculation, subtraction of 1 at theend may be omitted for the simplification of the circuit. Embodiment 20is an example of such simplification. Luminance signal component Y(s,t)at the position of GC color filter of row s, column t is calculated bythe equation (57) below.

    Y(s,t)=(GC(s,t)+1)×((YLPF(s,t)+1)/(GCLPF(s,t)+1))    (57)

Luminance signal component Y(s,t) at position (s,t) of color filter ofkind K (K is either MC, GY, MY or GC) is given by the equation (58)below.

    Y(s,t)=(K(s,t)+1)×((YLPF(s,t)+1)/(KLPF(s,t)+1))      (58)

Embodiment 21

FIG. 34 shows a block circuit diagram of the color video camera inembodiment 21. In FIG. 34, symbols which are the same as those in FIG.28 indicate the identical portions. Numerals 29, 30 represent a lookuptable for logarithm and a lookup table for power similar to those shownin FIG. 27 (embodiment 10).

The operation will now be described below. Luminance signal componentY(s,t) in case the kind of color filter of the pixel at position (s,t)is K (K is either MC, GY, MY or GC) is given, for example, by theequation (58) as described in embodiment 20. Now logarithmic conversionwith base x is applied to equation (58) as shown in equation (59), whererepresents power. ##EQU5##

In embodiment 21, arithmetic operation can be made using lookup tablesof small capacity similarly to embodiment 10 described before. Althoughthe above description is for the case of calculating a luminance signalbased on the equation of embodiment 20, it goes without saying that thecalculation by means of a lookup table for logarithm and a lookup tablefor power may be applied to embodiment 11.

Embodiment 22

FIG. 35 shows a block circuit diagram of the color video camera inembodiment 22. In FIG. 35, numeral 51 represents a lens, numeral 52represents a refracting prism, numerals 53, 54, 55 represent imagesensors, numeral 56 represents a red signal amplifier, numeral 57represents a green signal amplifier, numeral 58 represents a blue signalamplifier, numerals 59, 60, 61 represent A/D converters, numerals 62,63, 64 represent memories, numerals 65, 66, 67 represent low-passfilters (LPF), numeral 69 represents an adder, numeral 72 represents ademultiplexer, and numeral 75 represents an arithmetic logic unit. FIG.36 shows the internal composition of the arithmetic logic unit 75 whichhas demultiplexers 80, 81, a divider 82 and a multiplier 83.

The operation will now be described below. In FIG. 35, incident ray onthe lens 51 is decomposed into red, green and blue by the refractingprism 52, with the light rays of respective colors forming images on theimage sensors 53, 54, 55 which are formed by arranging photoelectrictransducers optically staggering from each other on a two-dimensionalplane. Each of the image sensors 53, 54, 55 mixes the signals of twoupper and lower adjacent pixels to give one signal output. The outputsignals of the image sensors 53, 54, 55 are amplified by the red signalamplifier 56, the green signal amplifier 57 and the blue signalamplifier 58, respectively, so that the ratio of the output signalsthereof becomes, in the case of NTSC system, R:G:B=0.30:0.59:0.11. Theamplified signals are converted form analog to digital signals by theA/D converters 59, 60, 61, respectively, to obtain R, G and B signals. Ris the red pixel signal, G is the green pixel signal and B is the bluepixel signal. G signal is stored in memory 62, R and B signals are mixedby the adder 69 and stored in memory 63. The demultiplexer 72 switchesalternately between G signal and R, B composite signal to produce asynthesized signal Y' which is stored in memory 64. FIG. 37, FIG. 38 andFIG. 39 partly illustrate the configuration of G signal, R, B compositesignal and Y' signal written in the memories 62, 63, 64. RB in thedrawings represents the R, B composite signal. The signals shown inthese drawings are smoothed by the low-pass filters 65, 66, 67. FIG. 40,FIG. 41 and FIG. 42 show the outputs of the low-pass filters 65, 66 and67, respectively. LPF in the drawing is a symbol representing a low-passfilter output.

The operation of the arithmetic logic unit 75 will be described below.The low-pass filter output of the synthesized signal Y' is fed to thedivider 82 as the dividend. The demultiplexer 81 switches to thelow-pass filter output of G signal if the pixel of interest is a greenpixel or to the low-pass filter output of R, B composite signal if thepixel of interest is a red, blue pixel, and the output thereof is fed tothe divider 82 as the divisor. The output of the divider 82 is suppliedto the multiplier 83 as the input. The demultiplexer 80 switches to theG signal if the pixel of interest is a green pixel or to the R, Bcomposite signal if the pixel of interest is a red, blue pixel, and theoutput thereof is fed to the multiplier 83. Thus the output of themultiplier 83 is obtained as Y signal at the pixel of interest.

In FIG. 37, luminance signal component Y (t) at the position of greenpixel of column t, for example, is calculated by equation (60) below.

    Y(t)=G(t)×(Y'LPF(t)/GLPF(t))                         (60)

Luminance signal component Y (t) at the position t of pixel of kind K (Kis either G or RB) is calculated by equation (61) below. In thisembodiment, letter t represents the coordinate of memory 64 shown inFIG. 39, or represents the coordinate of memory 62 shown in FIG. 37 incase the pixel of interest is G, or represents the coordinate of memory63 shown in FIG. 38 in case the pixel of interest is RB.

    Y(t)=K(t)×(Y'LPF(t)/KLPF(t))                         (61)

Embodiment 23

FIG. 43 shows a block circuit diagram of the color video camera inembodiment 23. In FIG. 43, numerals which are the same as those in FIG.35 indicate the identical portions and numeral 85 represents anarithmetic logic unit with the internal composition thereof being shownin FIG. 44. The arithmetic logic unit 85 has a demultiplexer 80, adivider 82 and a multiplier 83.

The operation will now be described below. In embodiment 23, G signaland R, B composite signal from the demultiplexer 72 are fed to thearithmetic logic unit 85. Low-pass filter output of the synthesizedsignal Y' is fed to the divider 82 as the dividend. The demultiplexer 80switches to the low-pass filter output of G signal if the pixel ofinterest is a green pixel, or to the low-pass filter output of R, Bcomposite signal if the pixel of interest is a red, blue pixel, and theoutput thereof is fed to the divider 82 as the divisor. The output ofthe divider 82 is supplied to the multiplier 83 as the input. Themultiplier 82 receives G signal as the input if the pixel of interest isa green pixel, or R, B composite signal if the pixel of interest is ared, blue pixel. As a result, output of the multiplier 83 is obtained asY signal at the pixel of interest. The rest of the operation is the sameas that of embodiment 22.

The principle of calculating Y signal in the above-mentioned embodiments22 and 23 will now be described below. This method is based on anassumption that the color does not change significantly in a localizedregion. This implies that ratios of signals of different colors (G, RB)to Y' signal are approximately equal to each other in the localizedregion. Ratios between signals of different colors G, RB and Y' signalin a localized region are given by the ratios between low-pass filteroutputs of G, RB and low-pass filter output of Y'.

At the position of G of column t as shown by equation (60), for example,Y(t) is obtained by multiplying G(t) by the ratio of Y' and G in thelocalized region (the ratio of the low-pass filter output of Y' signaland low-pass filter output of G signal).

In the conventional method of 3-chip CCD color camera based on spatialoffset, the purpose is set at improving the resolution. Although therearises no problem in the case of such objects that have green signal andred-blue composite signal in similar proportions, vertical lines appearin the case of objects which have significantly different proportions.Vertical lines have been reduced by passing the luminance signal througha low-pass filter in the prior art, though it has a problem of causingattenuation of harmonics in the luminance signal. According to thisinvention, Y signal is obtained by multiplying G(t) by the ratio of Y'and G in the localized region (the ratio of the low-pass filter outputof Y' signal and low-pass filter output of G signal), and consequentlyit is made possible to suppress the generation of vertical lines withoutattenuating the harmonics of the luminance signal.

Embodiment 24

Although the composition of the color video camera in embodiment 24 isthe same as that shown in FIG. 35, signal processing in the arithmeticlogic unit 75 is different, and Y signal is calculated by employing 1 ofLSB similarly to embodiment 3 described above. Specifically, Y(t) at theposition of G of column t is calculated by equation (62).

    Y(t)=(G(t)+1)×((Y'LPF(t)+1)/(GLPF(t)+1))-1           (62)

Luminance signal component Y(t) at the position t of a pixel of kind K(K is either G or RB) is calculated by equation (63) below. Letter trepresents the coordinate of memory 64 shown in FIG. 39 in thisembodiment, coordinate of memory 62 shown in FIG. 37 in case the pixelof interest is G, or coordinate of memory 63 shown in FIG. 38 in casethe pixel of interest is RB.

    Y(t)=(K(t)+1)×((Y'LPF(t)+1)/(KLPF(t)+1))-1           (63)

Embodiment 25

FIG. 45 shows a block circuit diagram of the color video camera inembodiment 25. In FIG. 45, symbols which are the same as those in FIG.35 indicate the identical portions, and numeral 27 represents acomparator similar to that shown in FIG. 22 (embodiment 4).

The operation will now be described below. The output signals of anappropriate pixel in the vicinity of the pixel of interest are suppliedfrom memories 62, 63 to the comparator 27. And it is determined that theimage has a high spatial frequency if the difference between the outputsignals from pixels of the same kind is greater than a particularthreshold, and it is determined that the image has a low spatialfrequency if the difference between the output signals is within thethreshold. In a portion of image having a high spatial frequency,luminance signal is calculated similarly to embodiment 22 and, in aportion of low spatial frequency, luminance signal is calculated fromthe weighted averaging value of the outputs of G signal and RB signal.

The arithmetic logic unit 75 operates similarly to embodiment 22 in theportion of high spatial frequency. In the portion of low spatialfrequency, luminance signal component Y(t) at the position where thereis no output signal of column t in FIG. 38, for example, is calculatedby equation (64) below.

    Y(t)=RB(t-1)/4+G(t)/2+RB(t+1)/4                            (64)

When the pixel of interest is located at position t, the kind of thepixel of interest is J (J is either G or RB), and the kind of the rightand left horizontal pixels of the pixel of interest is K (K is either Gor RB), luminance signal component Y(t) is calculated by equation (65).

    Y(t)=K(t-1)/4+J(t)/2+K(t+1)/4                              (65)

Embodiment 26

Although the composition of the color video camera in embodiment 26 isthe same as that of embodiment 25 (FIG. 45), signal processingoperations in the arithmetic logic unit 75 and in the comparator 27 aredifferent.

In embodiment 26, difference the between the output signals of the rightand left adjacent pixels of the pixel of interest is compared to aparticular threshold. And it is determined that the portion has highspatial frequency if the difference between the output signals isgreater than the threshold, and the operation of embodiment 22 iscarried out, and, it is determined that the portion has low spatialfrequency if the difference between the output signals is less than thethreshold, and the operation of embodiment 25 described above is carriedout.

For example, the result of the following calculation is compared to thethreshold at the position of G of column t in FIG. 37 and at theposition where there is no output signal of column t in FIG. 38, toselect one of the methods of generating luminance signal.

    |RB(t-1)-RB(t+1)|                        (66)

Assuming the position of the pixel of interest as t, the kind of theright and left adjacent pixels of the pixel of interest as K (K iseither G or RB), the result of the calculation below is compared to thethreshold to select one of the methods of generating luminance signal.

    |K(t-1)-K(t+1)|                          (67)

Embodiment 27

FIG. 46 shows a block circuit diagram of the color video camera inembodiment 27. In FIG. 46, symbols which are the same as those in FIG.35 indicate the identical portions, and numeral 28 represents a lookuptable for division similar to that shown in FIG. 23 (embodiment 6).

The operation of the lookup table for division 28 is the same as that inembodiment 6, and description thereof will be omitted here.

Embodiment 28

An embodiment where the method of calculation in embodiment 7 withrespect to embodiment 6 is applied to embodiment 27 described above isembodiment 28. The operation of the lookup table for division 28 inembodiment 28 is the same as that in embodiment 7, and descriptionthereof will be omitted here.

Embodiment 29

The composition of the color video camera in embodiment 29 is the sameas that of embodiment 22 (FIG. 35). In embodiment 29, a one-dimensionallow-pass filter is used as a digital filter which is made up of only bitshift circuits having weightings such as 1/8, 1/4. The construction ofthe one-dimensional low-pass filter is the same as that in embodiment 8(FIG. 26) and will not be described here.

Embodiment 30

Although the composition of the color video camera in embodiment 30 isthe same as that of embodiment 22 (FIG. 35), the method of calculatingthe luminance signal in the arithmetic logic unit 75 is different.

In embodiment 24, the luminance signal is obtained by adding 1 to eachof the multiplier, divisor and dividend and subtracting 1 from theresult of calculation at the end to minimize the calculation error, asshown in equations (62) and (63). However, as the number 1 is LSB whichhas no significant effect on the result of calculation, subtraction of 1at the end may be omitted for the simplification of the circuit.Embodiment 30 is an example of such simplification. Luminance signalcomponent Y(t) at the position of G of column t is calculated by theequation (68) below.

    Y(t)=(G(t)+1)×((Y'LPF(t)+1)/(GLPF(t)+1))             (68)

Luminance signal component Y(t) at position t of pixel of kind K (K iseither G or RB) is given by the equation (69) below.

    Y(t)=(K(t)+1)×((Y'LPF(t)+1)/(KLPF(t)+1))             (69)

Embodiment 31

FIG. 47 shows a block circuit diagram of the color video camera inembodiment 31. In FIG. 47, symbols which are the same as those in FIG.35 indicate the identical portions. Numerals 29, 30 represent a lookuptable for logarithm and a lookup table for power which are similar tothose shown in FIG. 27 (embodiment 10).

The operation will now be described below. Luminance signal componentY(t) in case the kind of the pixel at position t is K (K is either G orRB), for example, is given by equation (69) as described in embodiment30. Now logarithmic conversion with base x as shown in equation (70) isapplied to equation (69), where represents power. ##EQU6##

In embodiment 31, calculation can be made by using lookup tables ofsmall capacity as in embodiment 10 described before. Although the abovedescription is for the case of calculating luminance signal based on theequation of embodiment 30, it goes without saying that the calculationby means of a lookup table for logarithm and a lookup table for powermay be applied to embodiment 22.

Embodiment 32

FIG. 48 shows a block circuit diagram of the color video camera inembodiment 32. In FIG. 48, numerals which are the same as those in FIG.35 indicate the identical portions and will not be described here. InFIG. 48, numerals 92, 93, 94 represent two-dimensional memories, andnumerals 95, 96, 97 represent two-dimensional low-pass filters (LPF).

The operation will now be described below. The basic operation is thesame as that of embodiment 22. The configuration of G signal, R, Bcomposite signal and Y' signal written in the two-dimensional memories95, 96, 97 is partially illustrated in FIG. 49, FIG. 50 and FIG. 51. Thesignals shown in these drawings are smoothed by the two-dimensionallow-pass filters 95, 96, 97. FIG. 52, FIG. 53, FIG. 54 show the outputsof the two-dimensional low-pass filters 95, 96, 97. Letters LPF in thedrawing indicate the low-pass filter output.

Embodiment 32 is an example of using two-dimensional low-pass filtersinstead of one-dimensional low-pass filters of embodiment 22. In FIG.49, luminance signal component Y(s,t) at the position of green pixel ofrow s, column t, for example, is calculated by equation (71).

    Y(s,t)=G(s,t)×(Y'LPF(s,t)/GLPF(s,t))                 (71)

Luminance signal component Y(s,t) at the position (s,t) of a pixel ofkind K (K is either G or RB) is given by equation (72) below, where(s,t) represents the coordinates of the two-dimensional memory 94 shownin FIG. 51, the coordinates of the two-dimensional memory 92 shown inFIG. 49 in case the pixel of interest is G, and the coordinates of thetwo-dimensional memory 93 shown in FIG. 50 in case the pixel of interestis RB.

    Y(s,t)=K(s,t)×(Y'LPF(s,t)/KLPF(s,t))                 (72)

Embodiment 33

FIG. 55 shows a block circuit diagram of the color video camera inembodiment 33. In FIG. 55, numerals which are the same as those in FIG.48 indicate the identical portions and will not be described here. InFIG. 55, the arithmetic logic unit 85 has the same composition as thatof the arithmetic logic unit 85 in embodiment 23 described previously(FIG. 44). In this embodiment 33, a demultiplexer 72 feeds G signal andR, B composite signal to the arithmetic logic unit 85. In embodiment 33,two-dimensional low-pass filters are used instead of one-dimensionallow-pass filters of embodiment 23.

The principle of calculating the Y signal in embodiments 32, 33 isbasically the same as that in embodiments 22, 23, and is capable ofeliminating the modulated components of the color signal withoutreducing the harmonics of the luminance signal.

Embodiment 34

Although the composition of the color video camera in embodiment 34 isthe same as that of embodiment 32 (FIG. 48), the method of calculatingthe Y signal in the arithmetic logic unit 75 is different.

The arithmetic operation in the arithmetic logic unit 75 will bedescribed below. If each signal is made up of eight bits to representthe hue in 256 steps, for example, and value 1 of LSB is employed as aconstant, the luminance signal component Y(s,t) at the position of G ofrow s, column t is calculated by equation (73) as shown below.

    Y(s,t)=(G(s,t)+1)×((Y'LPF(s,t)+1)/(GLPF(s,t)+1))-1   (73)

The luminance signal component Y(s,t) at position (s,t) of pixel of kindK (K is either G or RB) is given by equation (74) below.

    Y(s,t)=(K(s,t)+1)×((Y'LPF(s,t)+1)/(KLPF(s,t)+1))-1   (74)

Embodiment 35

FIG. 56 shows a block circuit diagram of the color video camera inembodiment 35. In FIG. 56, symbols which are the same as those in FIG.48 indicate the identical portions and numeral 27 represents acomparator which is similar to that of FIG. 22 (embodiment 4).

The operation will now be described below. Difference between outputsignals of pixels of the same kind which are fed to the comparator 27from the two-dimensional memories 92, 93 is compared to a particularthreshold to determine whether the spatial frequency of the image ishigh or low. In a portion of the image with high spatial frequency, theluminance signal is calculated similarly to embodiment 32 and, in aportion of low spatial frequency, the luminance signal is calculatedfrom the weighted averaging value of the G signal and RB signal in thevicinity of the pixel of interest.

The arithmetic logic unit 75 operates similarly to that in embodiment 32in a portion of high spatial frequency. In a portion of low spatialfrequency, the luminance signal component Y(s,t) at the position of G ofrow s, column t in FIG. 49, and at a position where there is no outputsignal of row s, column t in FIG. 50, for example, is calculated byequation (75). ##EQU7##

Assuming the position of the pixel of interest as (s,t), kind of thepixel of interest as J (J is either G or RB), kind of the right and leftadjacent pixels of the pixel of interest as K (K is either G or RB),then the luminance signal component Y(s,t) is calculated by equation(76) below. ##EQU8##

Embodiment 36

Although the composition of the color video camera in embodiment 36 isthe same as that of embodiment 35 (FIG. 56), the signal processingoperations in the arithmetic logic unit 75 and in the comparator 27 aredifferent.

In embodiment 36, the difference between the output signals of the rightand left pixels, or between the output signals of the upper and lowerpixels, of the pixel of interest is compared to a particular threshold.And it is determined that the portion has high spatial frequency if thedifference between the output signals is greater than the threshold, andthe operation in embodiment 32 is carried out, and, it is determinedthat the portion has low spatial frequency if the difference between theoutput signals is less than the threshold, and accordingly the operationin embodiment 35 described above is carried out.

For example, result of the calculation described below is compared to aparticular threshold at the position of G at row s, column t in FIG. 49,and at the position where there is no output signal at row s, column tin FIG. 50, thereby to select one of the methods of generating theluminance signal.

    |RB(s,t-1)-RB(s,t+1)|                    (77)

    |G(s-1,t)-G(s+1,t)|                      (78)

Assuming the position of the pixel of interest as (s,t), the kind of thepixel of interest as J (J is either G or RB), and the kind of the rightand left adjacent pixel s of the pixel of interest as K (K is either Gor RB), then the results of the calculations below are compared to aparticular threshold to select one of the two methods of generating theluminance signal.

    |K(s,t-1)-K(s,t+1)|                      (79)

    |J(s-1,t)-J(s+1,t)|                      (80)

Embodiment 37

Although the composition of the color video camera in embodiment 37 isthe same as th at of embodiment 35 (FIG. 56), the signal processingoperations in the arithmetic logic unit 75 and in the comparator 27 aredifferent.

In embodiment 37, the difference between the outputs of the pixels ofthe same kind in the vicinity of the pixel of interest is compared to aparticular threshold. And it is determined that the portion has highspatial frequency if the difference is greater than the threshold, andthe operation of embodiment 32 is carried out, and, it is determinedthat the portion has low spatial frequency if the difference is lessthan the threshold, and accordingly the operation of embodiment 35described previously is carried out.

For example, the results of the calculations below are compared to aparticular threshold at the position of G of row s, column t in FIG. 49and at a position where there is no output signal of row s, column t inFIG. 50, to select one of the two methods of generating the luminancesignal.

    |RB(s,t-1)-RB(s,t+1)|                    (81)

    |G(s-1,t)-G(s+1,t)|                      (82)

    |RB(s-1,t-1)-RB(s+1,t+1)|                (83)

    |RB(s-1,t+1)-RB(s+1,t-1)|                (84)

Assuming that the position of the pixel of interest is (s, t), the kindof the pixel of interest as J (J is either G or RB), and the kind of theright and left adjacent pixels of the pixel of interest as K (K iseither G or RB), the results of the calculations below are compared to aparticular threshold to select one of the two methods of generating theluminance signal.

    |K(s,t-1)-K(s,t+1)|                      (85)

    |J(s-1,t)-J(s+1,t)|                      (86)

    |K(s-1,t-1)-K(s+1,t+1)|                  (87)

    |K(s-1,t+1)-K(s+1,t-1)|                  (88)

Embodiment 38

Although the composition of the color video camera in embodiment 38 isthe same as that of embodiment 35 (FIG. 56), the signal processingoperations in the arithmetic logic unit 75 and in the comparator 27 aredifferent.

In embodiment 38, the difference between the output signals of thediagonally adjacent pixels interposing the pixel of interest is comparedto a particular threshold. And it is determined that the portion hashigh spatial frequency if the difference between the output signals isgreater than the threshold, and the operation in embodiment 32 iscarried out, and, it is determined that the portion has low spatialfrequency if the difference between the output signals is less than thethreshold, and the operation in embodiment 35 described previously iscarried out.

For example, results of the calculations shown below are compared to thethreshold at the position of G at row s, column t in FIG. 49, and at aposition where there is no output signal of row s, column t in FIG. 50,thereby to select one of the two methods of generating the luminancesignal accordingly.

    |RB(s-1,t-1)-RB(s+1,t+1)|                (89)

    |RB(s+1,t-1)-RB(s-1,t+1)|                (90)

Assuming the position of the pixel of interest as (s,t), the kind of thediagonally adjacent pixels of the pixel of interest as J (J is either Gor RB), the results of the calculations shown below are compared to thethreshold, thereby to select one of the two methods of generating theluminance signal.

    |J(s-1,t-1)-J(s+1,t+1)|                  (91)

    |J(s+1,t-1)-J(s-1,t+1)|                  (92)

Embodiment 39

FIG. 57 shows a block circuit diagram of the color video camera inembodiment 39. In FIG. 57, symbols which are the same as those of FIG.48 indicate the identical portions, and numeral 28 represents a lookuptable for division which is similar to that of FIG. 23 (embodiment 6).

The operation in the lookup table for division 28 is the same as that ofembodiment 6, and will not be described here.

Embodiment 40

Application of the method of calculation in embodiment 7 with respect toembodiment 6 to the above embodiment 39 is this embodiment 40. Theoperation of the lookup table for division 28 in embodiment 40 is thesame as that of embodiment 7, and will not be described here.

Embodiment 41

The composition of the color video camera in embodiment 41 is the sameas that of embodiment 32 (FIG. 48). In embodiment 41, a two-dimensionallow-pass filter made up of only bit shift circuits of weightings such as1/8, 1/4, 1/2 is used as a digital filter. The composition of thetwo-dimensional low-pass filter is similar to that of embodiment 19(FIG. 33) where output Y'LPF(s, t) is obtained from the two-dimensionallow-pass filter in response to the synthesized signal Y', anddescription thereof will be omitted here. It should be noted here,however, that use of a two clock delay circuit instead of a one clockdelay circuit serves the purpose, because the two-dimensional low-passfilter for the Kth pixel at the position (s, t) of the pixel of interestis made by arranging the Kth pixels alternately every other pixel in thehorizontal direction.

Embodiment 42

Although the composition of the color video camera in embodiment 42 isthe same as that of embodiment 32 (FIG. 48), the method of calculatingthe luminance signal in the arithmetic logic unit 75 is different.

In embodiment 34, the luminance signal is obtained by adding 1 to eachof the multiplier, divisor and dividend and subtracting 1 from theresult of calculation at the end to minimize the calculation error, asshown in equations (73) and (74). However, because the number 1 is LSBwhich has no significant effect on the result of calculation,subtraction of 1 at the end may be omitted for the simplification of thecircuit. Embodiment 42 is an example of such simplification. Theluminance signal component Y(s,t) at the position of G of row s, columnt is calculated by equation (93) below.

    Y(s,t)=(G(s,t)+1)×((Y'LPF(s,t)+1)/(GLPF(s,t)+1))     (93)

The luminance signal component Y(s,t) at position (s,t) of pixel of kindK (K is either G or RB) is given by equation (94) below.

    Y(s,t)=(K(s,t)+1)×((Y'LPF(s,t)+1)/(KLPF(s,t)+1))     (94)

Embodiment 43

FIG. 58 shows a block circuit diagram of the color video camera inembodiment 43. In FIG. 58, symbols which are the same as those in FIG.48 indicate the identical portions. Numerals 29, 30 represent a lookuptable for logarithm and a lookup table for power similar to those shownin FIG. 27 (embodiment 10).

The operation will now be described below. The calculation of theluminance signal component Y(s,t) in case the kind of the pixel atposition (s,t) is K (K is either G or RB) is given, for example, by theequation (94) as described in embodiment 42. To this equation (94), thelogarithmic conversion with base x is applied as shown in equation (95),where represents power. ##EQU9##

In this embodiment 43, the arithmetic operation can be made using lookuptables of small capacity similarly to embodiment 10 described before.Although the above description is for the case of calculating aluminance signal based on the equation of embodiment 42, the calculationby means of a lookup table for logarithm and a lookup table for powermay be applied to embodiment 32.

Embodiment 44

FIG. 59 shows a block circuit diagram of the color video camera inembodiment 44. In FIG. 59, numerals which are the same as those in FIG.15 indicate the identical portions. In FIG. 59, numeral 45 represents alow-pass filter (LPF), numeral 46 represents a band-pass filter (BPF)and numeral 47 represents an adder.

The operation will now be described below. The basic operation from thelens 1 to the arithmetic logic unit 23 is the same as that of embodiment2. The output of the image sensor 2 is fed to the low-pass filter 45 toobtain YL signal as the output. The YL signal is similar to theluminance signal obtained with the prior art (see FIG. 2).

The operation of the arithmetic logic unit 23 will be described below.When the low-pass filter output of Y' signal is fed to the divider 25 asthe dividend (FIG. 16), the arithmetic operation similar to that inembodiment 2 is performed to obtain the output of the multiplier 26 asthe YH' signal of the pixel of interest.

In FIG. 17, YH' signal at the position of color filter GC of column t,for example, is calculated by equation (96) below.

    YH'(t)=GC(t)×(Y'LPF(t)/GCLPF(t))                     (96)

YH' signal at the position t of the color filter of kind K (K is eitherMC, GY, MY or GC) is calculated by equation (97) below, similarly toembodiment 2.

    YH'(t)=K(t)×(Y'LPF(t)/KLPF(t))                       (97)

The aperture correction is carried out by taking harmonics component YHfrom the YH' signal by means of the band-pass filter 46, combining theharmonics component YH and the YL signal in the adder 47 and therebyobtaining the luminance signal Y.

The principle of calculating the YH' signal in this embodiment 44 isbasically the same as the calculation of the Y signal in embodiment 2.Calculating the YH' signal in this way makes it possible to eliminatethe modulated components of the color signal without reducing theharmonics of the luminance signal. Consequently, the aperture correctionwithout unnatural enhancement is made possible by taking the harmonicscomponent YH from the YH' signal and mixing it with the YL signal.

Embodiment 45

Although the composition of the color video camera in embodiment 45 isthe same as that of embodiment 44 (FIG. 59), the method of calculatingthe YH' signal in the arithmetic logic unit 23 is different.

The arithmetic operation in the arithmetic logic unit 23 will bedescribed below. If each signal is made up of eight bits to representthe hue in 256 steps, for example, and value 1 of LSB is employed as aconstant, YH' signal at the position of color filter GC of column t iscalculated by equation (98) as shown below.

    YH'(t)=(GC(t)+1)×((Y'LPF(t)+1)/(GCLPF(t)+1))         (98)

The calculation of YH' signal at the position t of color filter of kindK (K is either MC, GY, MY or GC) is given by equation (99).

    YH'(t)=(K(t)+1)×((Y'LPF(t)+1)/(KLPF(t)+1))-1         (99)

Embodiment 46

FIG. 60 shows a block circuit diagram of the color video camera inembodiment 46. In FIG. 60, symbols which are the same as those in FIG.59 indicate the identical portions, and numeral 27 represents acomparator similar to that shown in FIG. 22 (embodiment 4).

The operation will now be described below. The output signals ofappropriate pixels in the vicinity of the pixel of interest are suppliedfrom the field memory 8 to the comparator 27. In a portion where theimage has a high spatial frequency, YH' signal is calculated similarlyto embodiment 44 and, in a portion of a low spatial frequency, YH'signal is calculated from the weighted averaging value of the outputs ofpixels of N kinds in the vicinity of the pixel of interest.

The arithmetic logic unit 23 operates similarly to embodiment 44 in theportion of high spatial frequency. In the portion of low spatialfrequency, YH' signal at the position of color filter of GC of column tin FIG. 17, and at the position where there is no output signal ofcolumn t in FIG. 18, for example, is calculated by equation (100) below,similarly to embodiment 4.

    YH'(t)=MY(t-1)/4+GC(t)/2+MY(t+1)/4                         (100)

The YH' signal, when the pixel of interest is located at position t,kind of the color filter of the pixel of interest is J and the kind ofthe color filters of the right and left adjacent pixels of the pixel ofinterest is K, is calculated by equation (101) below similarly toembodiment 4.

    YH'(t)=K(t-1)/4+J(t)/2+K(t+1)/4                            (101)

Embodiment 47

Although the composition of the color video camera in embodiment 47 isthe same as that of embodiment 46 (FIG. 60), the signal processingoperations in the arithmetic logic unit 23 and in the comparator 27 aredifferent.

In embodiment 47, the difference between the output signals of the rightand left adjacent pixels of the pixel of interest is compared to aparticular threshold. And it is determined that the portion has a highspatial frequency if the difference between the output signals isgreater than the threshold, and the operation in embodiment 44 iscarried out, and, it is determined that the portion has a low spatialfrequency if the difference between the output signals is less than thethreshold, and accordingly the operation in embodiment 46 is carriedout.

Results of the calculations by the same equations (20), (21) as inembodiment 5 are compared to a particular threshold, and the method ofcalculating the YH' signal is selected according to the result ofcomparison.

Embodiment 48

FIG. 61 shows a block circuit diagram of the color video camera inembodiment 48. In FIG. 61, symbols which are the same as those in FIG.59 indicate the identical portions, and numeral 28 represents a lookuptable for division similar to that shown in FIG. 23 (embodiment 6).

The operation of the lookup table for division 28 is the same as that inembodiment 6, and will not be described here.

Embodiment 49

Application of the calculation method of embodiment 7 with respect toembodiment 6 to the above embodiment 48 is this embodiment 49. Theoperation of the lookup table for division 28 in embodiment 49 is thesame as that of embodiment 7, and will not be described here.

Embodiment 50

The composition of the color video camera in embodiment 50 is the sameas that of embodiment 44 (FIG. 59). In embodiment 50, a one-dimensionallow-pass filter made up of only bit shift circuits of weightings such as1/8, 1/4 is used as a digital filter, The composition of theone-dimensional low-pass filter is similar to that of embodiment 8 (FIG.26), and description thereof will be omitted here.

Embodiment 51

Although the composition of the color video camera in embodiment 51 isthe same as that of embodiment 44 (FIG. 59), the method of calculatingthe YH' signal in the arithmetic logic unit 23 is different.

In embodiment 45, YH' signal is obtained by adding 1 to each of themultiplier, divisor and dividend and subtracting 1 from the result ofcalculation at the end to minimize the calculation error, as shown inequations (98) and (99). However, because the number 1 is LSB which hasno significant effect on the result of calculation, subtraction of 1 atthe end may be omitted for the simplification of the circuit. Embodiment51 is an example of such simplification, where YH' signal at theposition of color filter GC of column t is calculated by equation(102)below.

    YH'(t)=(GC(t)+1)×((Y'LPF(t)+1)/(GCLPF(t)+1))         (102)

The YH' signal at the position t of color filter of kind K is given byequation (103) below.

    YH'(t)=(K(t)+1)×((Y'LPF(t)+1)/(KLPF(t)+1))           (103)

Embodiment 52

FIG. 62 shows a block circuit diagram of the color video camera inembodiment 52. In FIG. 62, symbols which are the same as those in FIG.59 indicate the identical portions, and numerals 29, 30 represent alookup table for logarithm and a lookup table for power which aresimilar to those shown in FIG. 27 (embodiment 10).

The operation will now be described below. The calculation of the YH'signal in case the kind of the color filter at position t is K, forexample, is given by equation (103) as described in embodiment 51.Logarithmic conversion with base x as shown in equation (104) is appliedto equation (103), where represents power. ##EQU10##

In this embodiment 52, too, the calculation can be carried out withlookup tables of small capacity as in the case of embodiment 10described previously. Although the above description is for the case ofcalculating YH' signal based on the equation of embodiment 51, it goeswithout saying that the calculation by means of a lookup table forlogarithm and a lookup table for power may be applied to embodiment 44.

Embodiment 53

FIG. 63 shows a block circuit diagram of the color video camera inembodiment 53. In FIG. 63, numerals which are the same as those of FIG.28 indicate the identical portions, and will not be described here.

The operation will now be described below. Embodiment 53 is an exampleof using two-dimensional low-pass filters instead of one-dimensionallow-pass filters in embodiment 44. In FIG. 6, YH' signal at the positionof the color filter GC of row s, column t, for example, is calculated byequation (105).

    YH'(s,t)=GC(s,t)×(Y'LPF(s,t)/GCLPF(s,t))             (105)

The calculation of the YH' signal at the position (s,t) of color filterof kind K is given by equation (106) below.

    YH'(s,t)=K(s,t)×(Y'LPF(s,t)/KLPF(s,t))               (106)

The principle of calculating the YH' signal in this embodiment isbasically the same as that in embodiment 44. Similarly to the case ofembodiment 44, it is possible to eliminate the modulated components ofthe color signal without reducing the harmonics of the luminance signal,thereby enabling to carry out aperture correction without unnaturalenhancement.

Embodiment 54

Although the composition of the color video camera in embodiment 54 isthe same as that of embodiment 53 (FIG. 63), the method of calculatingthe Y signal in the arithmetic logic unit 32 is different.

The arithmetic operation in the arithmetic logic unit 32 will bedescribed below. If each signal is made up of eight bits to representthe hue in 256 steps, for example, and value 1 of LSB is employed as aconstant, YH' signal at the position of color filter GC of row s, columnt is calculated by equation (107) as shown below.

    YH'(s,t)=(GC(s,t)+1)×((Y'LPF(s,t)+1)/(GCLPF(s,t)+1))-1(107)

The calculation of the YH' signal at the position (s,t) of color filterof kind K is given by equation (108) below.

    YH'(s,t)=(K(s,t)+1)×((Y'LPF(s,t)+1)/(KLPF(s,t)+1))-1 (108)

Embodiment 55

FIG. 64 shows a block circuit diagram of the color video camera inembodiment 55. In FIG. 64, symbols which are the same as those in FIG.63 indicate the identical portions and numeral 27 represents acomparator which is similar to that of FIG. 22 (embodiment 4).

The operation will now be described below. The output signals ofappropriate pixels around the pixel of interest are fed to thecomparator 27 from the field memory 8. In a portion of the image with ahigh spatial frequency, YH' signal is calculated similarly to embodiment53 and, in a portion of low spatial frequency, YH' signal is calculatedfrom the weighted averaging value of the outputs of pixels of N kindsaround the pixel of interest.

The arithmetic logic unit 32 operates similarly to that in embodiment 53in the portion of high spatial frequency. In a portion of low spatialfrequency, YH' signal at position of color filter GC of row s, column tin FIG. 6, for example, is calculated by equation (109). ##EQU11##

Assuming the position of the pixel of interest as (s, t), kind of colorfilter of the pixel of interest as J, kind of the color filters of theright and left adjacent pixels of the pixel of interest as K, kind ofthe color filters of the upper and lower adjacent pixels of the pixel ofinterest as L, kind of the color filters of the diagonally adjacentpixels of the pixel of interest as M, then YH' signal is calculated byequation (110) below. ##EQU12##

Embodiment 56

Although the composition of the color video camera in embodiment 56 isthe same as that of embodiment 55 (FIG. 64), the signal processingoperations in the arithmetic logic unit 32 and in the comparator 27 aredifferent.

In embodiment 56, the difference between the output signals of the rightand left adjacent pixels of the pixel of interest or the differencebetween the output signals of the upper and lower adjacent pixels of thepixel of interest is compared to a particular threshold. And it isdetermined that the portion has high spatial frequency if the differencebetween the output signals is greater than the threshold, and theoperation of embodiment 53 is carried out, and it is determined that theportion has low spatial frequency if the difference between the outputsignals is less than the threshold, and accordingly the operation ofembodiment 55 described above is carried out.

Results of calculation of the same equations (37) through (40) as inembodiment 14 described previously are compared to a particularthreshold, and the method of calculating the YH' signal is selectedaccording to the result of comparison.

Embodiment 57

Although the composition of the color video camera in embodiment 57 isthe same as that of embodiment 55 (FIG. 64), the signal processingoperations in the arithmetic logic unit 32 and in the comparator 27 aredifferent.

In embodiment 57, the difference between pixels of the same spectralresponse characteristics around the pixel of interest is compared to aparticular threshold. And it is determined that the portion has a highspatial frequency if the difference is greater than the threshold, andthe operation of embodiment 53 is carried out, and, it is determinedthat the portion has a low spatial frequency if the difference is lessthan the threshold, and the operation of embodiment 55 described aboveis carried out.

Results of calculation of the same equations (41) through (48) as inembodiment 15 described previously are compared to a particularthreshold, and the method of calculating the YH' signal is selectedaccording to the result of comparison.

Embodiment 58

Although the composition of the color video camera in embodiment 58 isthe same as that of embodiment 55 (FIG. 64), the signal processingoperations in the arithmetic logic unit 32 and in the comparator 27 aredifferent.

In embodiment 58, the difference between the output signals ofdiagonally adjacent pixels interposing the pixel of interest is comparedto a particular threshold. And it is determined that the portion has ahigh spatial frequency if the difference between the output signals isgreater than the threshold, and the operation of embodiment 53 iscarried out, and, it is determined that the portion has a low spatialfrequency if the difference between the output signals is less than thethreshold, and accordingly the operation of embodiment 55 describedpreviously is carried out.

Results of calculation of the same equations (49) through (52) as inembodiment 16 described previously are compared to a particularthreshold, and the method of calculating the YH' signal is selectedaccording to the result of comparison.

Embodiment 59

FIG. 65 shows a block circuit diagram of the color video camera inembodiment 59. In FIG. 65, symbols which are the same as those in FIG.63 indicate the identical portions, and numeral 28 represents a lookuptable for division similar to that shown in FIG. 23 (embodiment 6).

The operation of the lookup table for division 28 is the same as that inembodiment 6, and will not be described here.

Embodiment 60

Application of the calculation method of embodiment 7 with respect toembodiment 6 to the above embodiment 59 is this embodiment 60. Theoperation of the lookup table for division 28 in embodiment 60 is thesame as that of embodiment 7, and will not be described here.

Embodiment 61

The composition of the color video camera in embodiment 61 is the sameas that of embodiment 53 (FIG. 63). In embodiment 61, a two-dimensionallow-pass filter made up of only bit shift circuits of weightings such as1/8, 1/4, 1/2 is used as a digital filter. The composition of thetwo-dimensional low-pass filter is similar to that of embodiment 19(FIG. 33), and the description thereof will be omitted.

Embodiment 62

Although the composition of the color video camera in embodiment 62 isthe same as that of embodiment 53 (FIG. 63), the method of calculatingthe YH' signal in the arithmetic logic unit 32 is different.

In embodiment 54, the luminance signal is obtained by adding 1 to eachof the multiplier, divisor and dividend and subtracting 1 from theresult of calculation at the end to minimize the calculation error, asexpressed by equations (107) and (108). However, because the number 1 isLSB which has no significant effect on the result of calculation,subtraction of 1 at the end may be omitted for the simplification of thecircuit. Embodiment 62 is an example of such simplification, where YH'signal at the position GC of row s, column t is calculated by equation(111) below.

    YH'(s,t)=(GC(s,t)+1)×((Y'LPF(s,t)+1)/(GCLPF(s,t)+1)) (111)

The YH' signal at the position (s, t) of the color filter of kind K ofthe pixel of interest is given by the equation (112) below.

    YH'(s,t)=(K(s,t)+1)×((Y'LPF(s,t)+1)/(KLPF(s,t)+1))   (112)

Embodiment 63

FIG. 66 shows a block circuit diagram of the color video camera inembodiment 63. In FIG. 66, symbols which are the same as those in FIG.63 indicate the identical portions. Numerals 29, 30 represent a lookuptable for logarithm and a lookup table for power which are similar tothose shown in FIG. 27 (embodiment 10).

The operation will now be described below. The calculation of the YH'signal in case the kind of the color filter of the pixel at position (s,t) is K is given by equation (112) as described in embodiment 62.Logarithmic conversion with base x as shown in equation (113) is appliedto equation (112), where represents power. ##EQU13##

In this embodiment 63, the calculation can be carried out with lookuptables of small capacity as in the case of embodiment 10. Although theabove description is for the case of calculating YH' signal based on theequation of embodiment 62, the calculation by means of a lookup tablefor logarithm and a lookup table for power may be applied to embodiment53.

Embodiment 64

FIG. 67 shows a block circuit diagram of the color video camera inembodiment 64. In FIG. 67, numerals which are the same as those in FIG.35 indicate the identical portions. In FIG. 67, numeral 68 represents alow-pass filter (LPF), numeral 70, 71 represent adders, numeral 73represents a demultiplexer. and numeral 74 represents a band-pass filter(BPF).

The operation will now be described below. The basic operation from thelens 1 to the arithmetic logic unit 75 is the same as that of embodiment22. The output signals of A/D converters 59, 61 are mixed in the adder71. The demultiplexer 73 switches the composite signal and the outputsignal of A/D converter 60 alternately to supply input to the low-passfilter 68, thereby to obtain YL signal as the output. The YL signal issimilar to the luminance signal obtained with the prior art (see FIG.3).

The operation of the arithmetic logic unit 75 will be described below.The composition of the arithmetic logic unit 75 is the same as that ofembodiment 22 (FIG. 36). When the low-pass filter output of Y' signal isfed to the divider 82 as the dividend, the arithmetic operation similarto that in embodiment 22 is performed to obtain the output of themultiplier 83 as the YH' signal.

In FIG. 37, YH' signal at the position of green pixel of column t, forexample, is calculated by equation (114) below.

    YH'(t)=G(t)×(Y'LPF(t)/GLPF(t))                       (114)

The YH' signal at the position t of a pixel of kind K is calculated byequation (115) below, similarly to embodiment 22.

    YH'(t)=K(t)×(Y'LPF(t)/KLPF(t))                       (115)

The aperture correction is performed by taking harmonics component YHfrom the YH' signal by means of the band-pass filter 74, combining theharmonics component YH and the YL signal in the adder 70 and therebyobtaining the luminance signal Y.

Embodiment 65

FIG. 68 shows a block circuit diagram of the color video camera inembodiment 65. In FIG. 68, numerals which are the same as those of FIG.67 or FIG. 43 indicate the identical portions. The composition of thearithmetic logic unit 85 is the same as that of embodiment 23 (FIG. 44).

In this embodiment, too, YH' signal which is similar to that ofembodiment 64 is obtained from the arithmetic logic unit 85, withaperture correction being carried out similarly to embodiment 64thereafter.

The principle of calculating the YH' signal in embodiments 64, 65 isbasically the same as the calculation of Y signal in embodiments 22, 23.When the YH' signal is calculated, it is made possible to eliminate themodulated components of the color signal without reducing the harmonicsof the luminance signal. Thus it is made possible to carry out aperturecorrection without unnatural enhancement, by taking harmonics componentYH from the YH' signal and mixing it wit h the YL signal.

Embodiment 66

Although the composition of the color video camera in embodiment 66 isthe same as that of FIG. 67, the signal processing operation in thearithmetic logic unit 75 is different. Specifically, YH'(t) at theposition of G of column t is calculated by equation (116).

    YH'(t)=(G(t)+1)×((Y'LPF(t)+1)/(GLPF(t)+1))-1         (116)

The calculation of the YH' signal at the position t of a pixel of kind Kis given by equation (117) below.

    YH'(t)=(K(t)+1)×((Y'LPF(t)+1)/(KLPF(t)+1))-1         (117)

Embodiment 67

FIG. 69 shows a block circuit diagram of the color video camera inembodiment 67. In FIG. 69, numerals which are the same as those in FIG.67 indicate the identical portions, and numeral 27 represents acomparator similar to that shown in FIG. 22 (embodiment 4).

The operation will now be described below. The output signals ofappropriate pixels in the vicinity of the pixel of interest are suppliedfrom memories 62, 63 to the comparator 27. In a portion where the imagehas a high spatial frequency, YH' signal is calculated similarly toembodiment 64 and, in a portion of a low spatial frequency, YH' signalis calculated from the weighted averaging value of the G signal and RBsignal.

The arithmetic logic unit 75 operates similarly to embodiment 64 in theportion of high spatial frequency. In the portion of low spatialfrequency, YH' signal at the position of G of column t in FIG. 37, andat the position where there is no output signal of column t in FIG. 38,for example, is calculated by equation (118) below.

    YH'(t)=RB(t-1)/4+G(t)/2+RB(t+1)/4                          (118)

The YH' signal, when the pixel of interest is located at position t,kind of the pixel of interest is J and the kind of the right and leftadjacent pixels of the pixel of interest is K, is calculated by equation(119) below.

    YH'(t)=K(t-1)/4+J(t)/2+K(t+1)/4                            (119)

Embodiment 68

Although the composition of the color video camera in embodiment 68 isthe same as that of embodiment 67 (FIG. 69), the signal processingoperations in the arithmetic logic unit 75 and in the comparator 27 aredifferent.

In embodiment 68, the difference between the output signals of the rightand left adjacent pixels of the pixel of interest is compared to aparticular threshold. And it is determined that the portion has a highspatial frequency if the difference between the output signals isgreater than the threshold, and the operation of embodiment 64 iscarried out, and it is determined that the portion has a low spatialfrequency if the difference between the output signals is less than thethreshold, and accordingly the operation of embodiment 67 describedabove is carried out.

Results of calculation of the same equations (66) and (67) as inembodiment 26 described previously are compared to a particularthreshold, and the method of calculating the YH' signal is selectedaccording to the result of comparison.

Embodiment 69

FIG. 70 shows a block circuit diagram of the color video camera inembodiment 69. In FIG. 70, symbols which are the same as those in FIG.67 indicate the identical portions, and numeral 28 represents a lookuptable for division similar to that shown in FIG. 23 (embodiment 6).

The operation of the lookup table for division 28 is the same as that inembodiment 6, and description thereof will be omitted.

Embodiment 70

An example in which the method of calculation in embodiment 7 withrespect to embodiment 6 is applied to embodiment 69 described above isthis embodiment 70. The operation of the lookup table for division 28 inembodiment 70 is the same as that in embodiment 7, and descriptionthereof will be omitted here.

Embodiment 71

The composition of the color video camera in embodiment 71 is the sameas that of embodiment 64 (FIG. 67). In embodiment 71, a one-dimensionallow-pass filter is used as a digital filter which is made up of only bitshift circuits having weightings such as 1/8, 1/4. The construction ofthe one-dimensional low-pass filter is similar to that in embodiment 8(FIG. 26) and will not be described here.

Embodiment 72

Although the composition of the color video camera in embodiment 72 isthe same as that of embodiment 64 (FIG. 67), the method of calculatingthe YH' signal in the arithmetic logic unit 75 is different.

In embodiment 66, YH signal is obtained by adding 1 to each of themultiplier, divisor and dividend and subtracting 1 from the result ofcalculation at the end to minimize the calculation error, as expressedby equations (116) and (117). However, because the number 1 is LSB whichhas no significant effect on the result of calculation, subtraction of 1at the end may be omitted for the simplification of the circuit.Embodiment 72 is an example of such simplification, where the YH' signalat the position of G of column t is calculated by equation (120) below.

    YH'(t)=(G(t)+1)×((Y'LPF(t)+1)/(GLPF(t)+1))           (120)

The calculation of the YH' signal at the position t of a pixel of kind Kis given by equation (121).

    YH'(t)=(K(t)+1)×((Y'LPF(t)+1)/(KLPF(t)+1))           (121)

Embodiment 73

FIG. 71 shows a block circuit diagram of the color video camera inembodiment 73. In FIG. 71, numerals which are the same as those in FIG.67 indicate the identical portions and numerals 29, 30 represent alookup table for logarithm and a lookup table for power which aresimilar to those shown in FIG. 27 (embodiment 10).

The operation will now be described below. YH' signal in case the kindof the pixel at position t is K, for example, is given by equation (121)as described in embodiment 72. To the equation (121), logarithmicconversion with base x as shown in equation (122) is applied, whererepresents power. ##EQU14##

In embodiment 73, too, the calculation can be carried out by usinglookup tables of small capacity as in embodiment 10 describedpreviously. Although the above description is for the case ofcalculating YH' signal based on the equation of embodiment 72, it goeswithout saying that the calculation by means of a lookup table forlogarithm and a lookup table for power may be applied to embodiment 64.

Embodiment 74

FIG. 72 shows a block circuit diagram of the color video camera inembodiment 74. In FIG. 72, numerals which are the same as those in FIG.67 indicate the identical portions and will not be described here. InFIG. 72, numerals 92, 93, 94 represent two-dimensional memories, andnumerals 95, 96, 97 represent two-dimenisional low-pass filters (LPF).The composition of the arithmetic logic unit 75 is the same as that ofembodiment 22 (see FIG. 36).

The operation will now be described below. The basic operation is thesame as that of embodiment 64. Similarly to embodiment 32, thetwo-dimensional memories 92, 93, 94 store G signal, RB composite signaland Y' signal written therein (see FIG. 49, FIG. 50, FIG. 51), andtwo-dimensional low-pass filter outputs (see FIG. 52, FIG. 53, FIG. 54)are obtained from the two-dimensional low-pass filters 95, 96, 97.

Embodiment 74 is an example of using two-dimensional low-pass filtersinstead of one-dimensional low-pass filters in embodiment 64. In FIG.49, YH' signal at the position of green pixel of row s, column t, forexample, is calculated by equation (123).

    YH'(s,t)=G(s,t)×(Y'LPF(s,t)/GLPF(s,t))               (123)

The calculation of YH' signal at position (s,t) of pixel of kind K (K iseither G or RB) is given by equation (124) below, similarly toembodiment 32.

    YH'(s,t)=K(s,t)×(Y'LPF(s,t)/KLPF(s,t))               (124)

Embodiment 75

FIG. 73 shows a block circuit diagram of the color video camera inembodiment 75. In FIG. 73, numerals which are the same as those in FIG.72 indicate the identical portions and will not be described here. InFIG. 73, the arithmetic logic unit 85 has the same composition as thatof the arithmetic logic unit 85 in embodiment 23 described previously(FIG. 44). In this embodiment 75, the demultiplexer 72 feeds G signaland R, B composite signal to the arithmetic logic unit 85. In embodiment75, two-dimensional low-pass filters are used instead of one-dimensionallow-pass filters in embodiment 65.

The principle of calculating Y signal in embodiments 74, 75 is basicallythe same as that in embodiments 64, 65, and is capable of eliminatingthe modulated components of the color signal without reducing theharmonics of the luminance signal to calculate the YH' signal, therebyenabling it to carry out the aperture correction without unnaturalenhancement by taking the harmonics component YH from the YH' signal andmixing it with YL signal.

Embodiment 76

Although the composition of the color video camera in embodiment 76 isthe same as that of FIG. 72, the signal processing operation in thearithmetic logic unit 75 is different. Specifically, YH' (s,t) at theposition of G at (s, t) is calculated by equation (125).

    YH'(s,t)=(G(s,t)+1)×((Y'LPF(s,t)+1)/(GLPF(s,t)+1))-1 (125)

The calculation of the YH' signal at the position (s, t) of a pixel ofkind K is given by equation (126) below.

    YH'(s,t)=(K(s,t)+1)×((Y'LPF(s,t)+1)/(KLPF(s,t)+1))-1 (126)

Embodiment 77

FIG. 74 shows a block circuit diagram of the color video camera inembodiment 77. In FIG. 74, numerals which are the same as those in FIG.72 indicate the identical portions, and numeral 27 represents acomparator similar to that shown in FIG. 22 (embodiment 4).

The operation will now be described below. The output signals ofappropriate pixels in the vicinity of the pixel of interest are suppliedfrom two-dimensional memories 92, 93 to the comparator 27. In a portionwhere the image has a high spatial frequency, YH' signal is calculatedsimilarly to embodiment 74 and, in a portion of a low spatial frequency,YH' signal is calculated from the weighted averaging value of theoutputs of N kinds of pixels in the vicinity of the pixel of interest.

The arithmetic logic unit 75 operates similarly to embodiment 74 in theportion of high spatial frequency. In the portion of a low spatialfrequency, YH' signal at the position of G of row s, column t in FIG.49, and at the position where there is no output signal of row s, columnt in FIG. 50, for example, is calculated by equation (127) below.##EQU15##

The YH' signal, when the pixel of interest is located at position (s,t), kind of the pixel of interest is J and the kind of the right andleft adjacent pixels of the pixel of interest is K, is calculated byequation (128) below. ##EQU16##

Embodiment 78

Although the composition of the color video camera in embodiment 78 isthe same as that of embodiment 77 (FIG. 74), the signal processingoperations in the arithmetic logic unit 75 and in the comparator 27 aredifferent.

In embodiment 78, the difference between the output signals of the rightand left adjacent pixels of the pixel of interest or the differencebetween the output signals of the upper and lower adjacent pixels of thepixel of interest is compared to a particular threshold. And it isdetermined that the portion has a high spatial frequency if thedifference between the output signals is greater than the threshold, andthe operation of embodiment 74 is carried out, and, it is determinedthat the portion has a low spatial frequency if the difference betweenthe output signals is less than the threshold, and the operation ofembodiment 77 described above is carried out.

Results of the calculations by the same equations (77) through (80) asin embodiment 36 described previously are compared to a particularthreshold to select one of the methods of generating YH' signalaccording to the result of comparison.

Embodiment 79

Although the composition of the color video camera in embodiment 79 isthe same as that of embodiment 77 (FIG. 74), the signal processingoperations in the arithmetic logic unit 75 and in the comparator 27 aredifferent.

In embodiment 79, the difference between the outputs of the pixels ofthe same kind in the vicinity of the pixel of interest is compared to aparticular threshold. And it is determined that the portion has a highspatial frequency if the difference is greater than the threshold, andthe operation of embodiment 74 is carried out, and, it is determinedthat the portion has a low spatial frequency if the difference is lessthan the threshold, and the operation of embodiment 77 described aboveis carried out.

Results of the calculations by the same equations (81) through (88) asin embodiment 37 described previously are compared to a particularthreshold to select one of the methods of generating YH' signalaccording to the result of comparison.

Embodiment 80

Although the composition of the color video camera in embodiment 80 isthe same as that of embodiment 77 (FIG. 74), the signal processingoperations in the arithmetic logic unit 75 and in the comparator 27 aredifferent.

In embodiment 80, the difference between the output signals of thediagonally adjacent pixels interposing is compared to a particularthreshold. And it is determined that the portion has a high spatialfrequency if the difference between the output signals is greater thanthe threshold, and the operation of embodiment 74 is carried out, and,it is determined that the portion has a low spatial frequency if thedifference between the output signals is less than the threshold, andthe operation of embodiment 77 described above is carried out.

Results of the calculations by the same equations (89) through (92) asin embodiment 38 described previously are compared to a particularthreshold to select one of the methods of generating YH' signalaccording to the result of comparison.

Embodiment 81

FIG. 75 shows a block circuit diagram of the color video camera inembodiment 81. In FIG. 75, symbols which are the same as those in FIG.72 indicate the identical portions, and numeral 28 represents a lookuptable for division similar to that shown in FIG. 23 (embodiment 6).

The operation of the lookup table for division 28 is the same as that inembodiment 6, and description thereof will be omitted.

Embodiment 82

An example in which the method of calculation in embodiment 7 withrespect to embodiment 6 is applied to embodiment 81 described above isthis embodiment 82. The operation of the lookup table for division 28 inembodiment 82 is the same as that in embodiment 7, and descriptionthereof will be omitted.

Embodiment 83

The composition of the color video camera in embodiment 83 is similar tothat of embodiment 74 (FIG. 72). In embodiment 83, a two-dimensionallow-pass filter made up of only bit shift circuits of weightings such as1/8, 1/4, 1/2 is used as a digital filter. The composition of thetwo-dimensional low-pass filter is similar to that of embodiment 19(FIG. 33) where output Y'LPF(s, t) is obtained from the two-dimensionallow-pass filter in response to the synthesized signal Y', anddescription thereof will be omitted. It should be noted here, however,that use of a two clock delay circuit instead of a one clock delaycircuit serves the purpose, because the two-dimensional low-pass filterfor the Kth pixel at the position (s, t) of the pixel of interest ismade by arranging the Kth pixels alternately every other pixel, in thehorizontal direction.

Embodiment 84

Although the composition of the color video camera in embodiment 84 isthe same as that of embodiment 74 (FIG. 72), the method of calculatingthe YH' signal in the arithmetic logic unit 75 is different.

In embodiment 76, luminance signal is obtained by adding 1 to each ofthe multiplier, divisor and dividend and subtracting 1 from the resultof calculation at the end to minimize the calculation error, asexpressed by the equations (125) and (126). However, because the number1 is LSB which has no significant effect on the result of calculation,subtraction of 1 at the end may be omitted for the simplification of thecircuit. Embodiment 84 is an example of such simplification, and YH'signal at the position of G of row s, column t is calculated by equation(129) below.

    YH'(s,t)=(G(s,t)+1)×((Y'LPF(s,t)+1)/(GLPF(s,t)+1))   (129)

YH' signal at position (s,t) of pixel of kind K is given by the equation(130) below.

    YH'(s,t)=(K(s,t)+1)×((Y'LPF(s,t)+1)/(KLPF(s,t)+1))   (130)

Embodiment 85

FIG. 76 shows a block circuit diagram of the color video camera inembodiment 85. In FIG. 76, symbols which are the same as those in FIG.72 indicate the identical portions. Numerals 29, 30 represent a lookuptable for logarithm and a lookup table for power similar to those shownin FIG. 27 (embodiment 10).

The operation will now be described below. The calculation of the YH'signal in case the kind of the pixel at position (s,t) is K is given,for example, by the equation (130) as described in embodiment 84. Tothis equation (130), the logarithmic conversion with base x is appliedas expressed by equation (131), where represents power. ##EQU17##

In this embodiment 85, the arithmetic operation can be carried out byusing lookup tables of small capacity similarly to embodiment 10described before. Although the above description is for the case ofcalculating YH' signal based on the equation of embodiment 84, thecalculation by means of a lookup table for logarithm and a lookup tablefor power may be applied to embodiment 74.

Although the image sensor in the above embodiments is of a type whichreads two upper and lower adjacent pixels by mixing them, they may be ofa type which reads every pixel separately. The criterion of determiningthe level of spatial frequency of an image is also not restricted to theembodiments described above and may be otherwise.

Although descriptions of the above embodiments assume complementarycolors for the kind of color filters in the embodiments which use asingle image sensor, color filters of primary colors or combination of aprimary color and a complementary color may be used. Although examplesusing field memories for the color separation memories are given, linememories of the number of lines required for the processing of low-passfilters may be used.

Although the synthesized signal Y' of G signal and R, B composite signalis synthesized by a demultiplexer in the embodiments by using threetypes of image sensors, use of adders or other means may be used tosynthesize the signals.

Although harmonics component is taken from the luminance signal by meansof the band-pass filter in the embodiment where the aperture correctionis carried out, the high-pass filter may be used for this purpose.Embodiments where the YL signal is processed as digital signal aregiven, but it may be processed as analog signal.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within metesand bounds of the claims, or equivalence of such metes and boundsthereof are therefore intended to be embraced by the claims.

What is claimed is:
 1. A color video camera to obtain color images,comprising:a spectral optical system which decomposes an incident rayinto N, where N is an integer, kinds of light; N pieces of image sensorscomposed of photoelectric transducers arranged on a two-dimensionalplane being optically staggered to each other; low-pass filters whereinN kinds of signals generated by adjusting a gain of the outputs of theimage sensors are supplied as an input to obtain N kinds of outputs fromthe 1st through Nth; and means for calculating a luminance signalcomponent wherein a output signal of a Kth (1≦K≦N) pixel of interest ismultiplied by a ratio of the low-pass filter output of a synthesizedsignal of pixels of the respective kinds at the coordinates of the Kthpixel of interest to the Kth low-pass filter output at coordinates ofthe Kth pixel of interest, thereby to obtain the luminance signalcomponent and to improve resolution without attenuating harmonics of theluminance signal component.
 2. A color video camera to obtain colorimages, comprising:a spectral optical system which decomposes anincident ray into N, where N is an integer, kinds of light; N pieces ofimages sensors composed of photoelectric transducers arranged on atwo-dimensional plane being optically staggered to each other; low-passfilters where N kinds of signals generated by adjusting a gain ofoutputs of the image sensors are supplied as an input, to obtain N kindsof outputs from the 1st through Nth; and means for calculating aluminance signal component wherein an output signal of a Kth (1≦K≦N)pixel of interest plus a constant value is multiplied by a ratio of thelow-pass filter output of a synthesized signal of pixels of therespective kinds at the coordinates of the Kth pixel of interest plusthe constant value to a Kth low-pass filter output at coordinates of theKth pixel of interest plus the constant value, and the constant value issubtracted from the result of the multiplication and division, therebyto obtain the luminance signal component with improved resolution andunattenuated harmonics.
 3. A color video camera to obtain color images,comprising:a spectral optical system which decomposes an incident rayinto N, where N is an integer, kinds of light; N pieces of image sensorscomposed of photoelectric transducers arranged on a two-dimensionalplane being optically staggered to each other; low-pass filters whereinN kinds of signals generated by adjusting a gain of outputs of the imagesensors are supplied as an input to obtain N kinds of outputs from the1st through Nth; and first calculating means for calculating theluminance signal component wherein, in a portion of an image having ahigh spatial frequency, an output signal of a Kth (1≦K≦N) pixel ofinterest is multiplied by a ratio of a low-pass filter output of asynthesized signal of pixels of the respective kinds at the coordinatesof the Kth pixel of interest to a Kth low-pass filter output atcoordinates of the Kth pixel of interest, thereby to obtain theluminance signal component; and second calculating means for calculatingthe luminance signal component from a weighted averaging value ofoutputs of N kinds of pixels in a vicinity of the Kth pixel of interest,in a portion of the image having a low spatial frequency to improveresolution of the luminance signal component without attenuatingharmonics.
 4. A color video camera of claim 3, further comprising:meansfor selecting the first or the second calculating means, depending onwhether a difference between outputs of the right and left adjacentpixels of the Kth pixel of interest is greater than a predeterminedthreshold.
 5. A color video camera of claim 1, wherein a fractionalproduct of the calculating means is composed of a lookup table fordivision, while in the fractional product, if an input to the table isn-bit data, the input is checked to see if a most significant bitthereof is 1 and, if it is 0, a next bit is checked subsequentlyeventually stopping at an nth bit, and a bit shift operation is carriedout after the check, thereby using effective n-bit data with 0 bitsremoved therefrom as the input to the lookup table for division.
 6. Acolor video camera as claimed in claim 5, whereincontents of the lookuptable for division are increased by n bits through a bit shift operationon a result of the dividing operation, to take an integral part anddiscarding a fractional part, while applying a bit shift operation to aresult of calculation which uses the value, to reduce it by n bits toreturn it to an original number of bits, thereby taking the integralpart as a result of the calculation.
 7. A color video camera of claim 1,whereinthe calculating means applies logarithmic conversion to afractional component and uses a lookup table for logarithm and a lookuptable for power.
 8. A color video camera of claim 1, whereineach of thelow-pass filters includes a plurality of bit shift circuits and an adderwhich takes in outputs of the bit shift circuits as an input thereof. 9.A color video camera to obtain color images, comprising:a spectraloptical system which decomposes an incident ray into N, where N is aninteger, kinds of light; N pieces of image sensors composed ofphotoelectric transducers arranged on a two-dimensional plane beingoptically staggered to each other; low-pass filters wherein N kinds ofsignals generated by adjusting a gain of outputs of the image sensorsare supplied as an input, to obtain N kinds of outputs from the 1stthrough Nth; and means for calculating a luminance signal componentwherein an output signal of a Kth (1≦K≦N) pixel of interest plus aconstant value is multiplied by a ratio of a low-pass filter output of asynthesized signal of pixels of the respective kinds at coordinates ofthe Kth pixel of interest plus the constant value to a Kth low-passfilter output at coordinates of the Kth pixel of interest plus theconstant value, thereby to obtain the luminance signal component withimproved resolution and unattenuated harmonics.
 10. A color video cameraof claim 9, whereinthe calculating means applies logarithmic conversionto a fractional component and uses a lookup table for logarithm and alookup table for power.
 11. A color video camera to obtain color images,comprising:a spectral optical system which decomposes an incident rayinto N, where N is an integer, kinds of light; N pieces of image sensorscomposed of photoelectric transducers arranged on a two-dimensionalplane being optically staggered to each other; two-dimensional low-passfilters wherein N kinds of signals generated by adjusting a gain ofoutputs of the image sensors are supplied as inputs to obtain N kinds ofoutputs from the 1st through Nth; and means for calculating a luminancesignal component wherein an output signal of a Kth (1≦K≦N) pixel ofinterest is multiplied by a ratio of the two-dimensional low-pass filteroutput of a synthesized signal of pixels of the respective kinds atcoordinates of the Kth pixel of interest to the Kth two-dimensionallow-pass filter output at the coordinates of the Kth pixel of interest,thereby to obtain the luminance signal component and to improveresolution without attenuating harmonics of the luminance signalcomponent.
 12. A color video camera to obtain color images, comprising:aspectral optical system which decomposes an incident ray into N, whereinN is an integer, kinds of light; N pieces of image sensors composed ofphotoelectric transducers arranged on a two-dimensional plane beingoptically staggered to each other; two-dimensional low-pass filterswherein N kinds of signals generated by adjusting a gain of outputs ofthe image sensors are supplied as an input, to obtain N kinds of outputsfrom the 1st through Nth; and means for calculating a luminance signalcomponent wherein an output signal of a Kth (1≦K≦N) pixel of interestplus a constant value is multiplied by a ratio of a two-dimensionallow-pass filter output of a synthesized signal of pixels of therespective kinds at coordinates of the Kth pixel of interest plus theconstant value, and the constant value is subtracted from a result of amultiplication and division, thereby to obtain the luminance signalcomponent with improved resolution and unattenuated harmonics.
 13. Acolor video camera to obtain color images, comprising:a spectral opticalsystem which decomposes an incident ray into N, where N is an integer,kinds of light; N pieces of image sensors composed of photoelectrictransducers arranged on a two-dimensional plane being opticallystaggered to each other; two-dimensional low-pass filters wherein Nkinds of signals generated by adjusting a gain of outputs of the imagesensors are supplied as an input to obtain N kinds of outputs from the1st through Nth; and first calculating means for calculating a luminancesignal component wherein, in a portion of an image having a high spatialfrequency, an output signal of a Kth (1≦K≦N) pixel of interest ismultiplied by a ratio of a two-dimensional low-pass filter output of asynthesized signal of pixels of the respective kinds at coordinates ofthe Kth pixel of interest to a Kth two-dimensional low-pass filteroutput at coordinates of the Kth pixel of interest thereby to obtain theluminance signal component; and second calculating means for calculatingthe luminance signal component from a weighted averaging value ofoutputs of N kinds of pixels in a vicinity of the Kth pixel of interest,in a portion of the image having a low spatial frequency to improveresolution of the luminance signal component without attenuatingharmonics.
 14. A color video camera of claim 13 further comprising:meansfor selecting the first or the second calculating means, depending onwhether either a difference between outputs of right and left adjacentpixels of the Kth pixel of interest or a difference between outputs ofupper and lower adjacent pixels of the Kth pixel of interest is greaterthan a predetermined threshold.
 15. A color video camera of claim 13,further comprising:means for selecting the first or the secondcalculating means, depending on whether a difference between outputs ofpixels of the same kind in a vicinity of the Kth pixel of interest isgreater than a predetermined threshold.
 16. A color video camera ofclaim 13, further comprising:means for selecting the first or the secondcalculating means, depending on whether either a difference betweenoutputs of an upper-left diagonally adjacent pixel and a lower-rightdiagonally adjacent pixel of the Kth pixel of interest or a differencebetween outputs of a lower-left diagonally adjacent pixel and anupper-right diagonally adjacent pixel of the Kth pixel of interest isgreater than a predetermined threshold.
 17. A color video camera ofclaim 11, whereina fractional product of the calculating means iscomposed of a lookup table for division, while in the fractionalproduct, if an input to a table is n-bit data, the input is checked tosee if a most significant bit thereof is 1 and, if it is 0, a next bitis checked subsequently eventually stopping at an nth bit, and a bitshift operation is carried out after the check, thereby using effectiven-bit data with 0 bits removed therefrom, as the input to the lookuptable for division.
 18. A color video camera as claimed in claim 17,whereincontents of the lookup table for division are increased by n bitsthrough a bit shift operation on a result of the dividing operation, totake an integral part and discarding the fractional part, while applyinga bit shift operation to a result of calculation which uses the value,to reduce it by n bits to return it to an original number of bits,thereby taking the integral part as a result of the calculation.
 19. Acolor video camera of claim 11, whereinthe calculating means applieslogarithmic conversion to a fractional component and uses a lookup tablefor logarithm and a lookup table for power.
 20. A color video camera ofclaim 11, whereineach of the low-pass filters includes a plurality ofbit shift circuits an a plurality of adders which take in outputs of thebit shift circuits as an input thereof.
 21. A color video camera toobtain color images, comprising:a spectral optical system whichdecomposes an incident ray into N, where N is an integer, kinds oflight; N pieces of image sensors composed of photoelectric transducersarranged on a two-dimensional plane being optically staggered to eachother; two-dimensional low-pass filters wherein N kinds of signalsgenerated by adjusting a gain of outputs of the image sensors aresupplied as an input, to obtain N kinds of outputs from the 1st throughNth; and means for calculating a luminance signal component wherein anoutput signal of a Kth (1≦K≦N) pixel of interest plus a constant valueis multiplied by a ratio of a two-dimensional low-pass filter output ofa synthesized signal of pixels of the respective kinds at coordinates ofthe Kth pixel of interest plus the constant value to a Kthtwo-dimensional low-pass filter output at coordinates of the Kth pixelof interest plus the constant value, thereby to obtain the luminancesignal component with improved resolution and unattenuated harmonics.22. A color video camera of claim 21, whereinthe calculating meansapplies logarithmic conversion to a fractional component and uses alookup table for logarithm and a lookup table for power.